Data Release Four of LAMOST Medium-Resolution Spectroscopic Survey (MRS)

Section 1. Overview

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is a Chinese national scientific research facility operated by the National Astronomical Observatories, Chinese Academy of Sciences. It is a special reflecting Schmidt telescope with 4000 fibers in a field of view of 20 deg2 in the sky. Since October 2018, LAMOST started the second stage survey program (LAMOST II), which contains both low- and medium-resolution spectroscopic surveys. LAMOST II takes about 50% nights (dark/gray nights) to continue the previous low-resolution spectroscopic survey, and another 50% nights (bright/gray nights) to conduct the medium-resolution survey (MRS)[1]. For LAMOST MRS, it includes two surveys, i.e., the time-domain and the non time-domain surveys. The main purpose of the time-domain survey is to investigate variable targets, which were repeatedly observed in several observation nights, but targets of the non time-domain survey were observed only in one night in general. 

This time,  31,043,138 single exposure spectra and 8,333,131 coadded spectra were obtained, which were written into 4,301,476 FITS files. For objects close to the moon, spectra may be affected by the moon, thus targets with the angular distances to the moon less than 10 degrees were not observed. For the non time-domain survey, there are totally 2,318,264 coadded spectra published, and for the time-domain survey, 8,711,580 single exposure spectra were released. The data products of this data release can be available from the website http://www.lamost.org/dr10/V2.0/, and they include：

1. Spectra. - For a target of MRS, we can get two spectra within an exposure, including a blue (B) and a red (R) band spectrum, and their wavelength ranges are [4950 Å, 5350 Å] and [6300 Å, 6800 Å], respectively. Generally, each object was observed several times, and we would obtain the coadded B and R band spectra by combing the single exposure spectra. Few targets, however, lack of the spectral data of either band for some reason like the wavelength calibration, only one even no coadded spectra exists in their FITS file. For single exposure and coadd spectra, they both have a resolution of 7500 respectively at 5163 Å (blue) and 6593 Å (red). 

2.   Spectroscopic Parameter Catalogs. - In this data release, five spectroscopic parameter catalogs are published, and they are the LAMOST MRS General Catalog, the LAMOST MRS Parameter Catalog, the LAMOST MRS Multiple Epoch Catalog, the LAMOST MRS Observed Plate Information Catalog, and the LAMOST MRS Input Catalog, respectively. More than a hundred parameters are included in these catalogs, such as right ascension, declination, signal to noise ratio (S/N), Gaia source identifier and magnitudes, atmospheric parameters (effective temperature, surface gravity, and metallicity), radial velocity, element abundance, and dome seeing.

In the following section 2, we introduce the released FITS file in detail, and present four parameter catalogs in section 3.

Section 2. FITS File

2.1 Designation

In this data release, 4,301,476 FITS files are published on-line which include 31,043,138 single exposure spectra and 8,333,131 coadded spectra, and they are named in the form of “med-MMMMM-YYYY_spXX-FFF.fits”. “MMMMM”, “YYYY”, “XX”, and “FFF” represent the local modified Julian day (LMJD), which is a non-negative integer, the plan identity string (PLANID), the spectrograph identity number which is between 1 and 16, and the fiber identity number which is in the range of 1 to 250, respectively.

2.2 Structure

For each of LAMOST targets, it has m (m <= n) B band and t (t <= n) R band single exposure spectra if it has n time exposures. If m and t are all larger than 0, the target has a B band and a R band coadded spectra, but no coadded spectrum is provided in the FITS file if at least one of m and n is equal to 0. 

In a LAMOST median resolution (MR) FITS file, extension 0 is the primary HDU which is not followed by a primary data array, and extension 1 and 2 restore the coadded B and R band spectra, respectively. For extensions from 3 to m + 2, they save the information of m B band spectra obtained within n time exposures, and they are named as “B-lmjm”, where “lmjm” is the local modified Julian minutes at the beginning of each exposure. For following extensions from m+3 to m+t+2, t R band spectra of n time exposures are stored, and they are called as “R-lmjm”. 

In following section 2.3, 2.4 and 2.5, we introduce the primary extension, extension 1 and 2, and other single exposure extensions.

2.3 Primary Extension

In this section, we describe the primary extension. Not like the low resolution FITS file, this extension of MR FITS file only has a file header, and it do not have following data array.

In the header file, we divided keywords into seven groups, and they are mandatory keywords, file information keywords, telescope parameter keywords, observation parameter keywords, spectrograph parameter keywords, weather condition keywords, and data reduction parameters keywords, respectively. We will explain keywords of each group from subsection 2.3.1 to 2.3.7.

2.3.1 Mandatory Keywords

Mandatory keywords are required in every Header Data Unit (HDU), and their value must be written in fixed format.

SIMPLE  =                    T /Primary Header created by MWRFITS v1.11b
BITPIX  =                   16 /
NAXIS   =                    0 /
EXTEND  =                    T /Extensions may be present  

SIMPLE Keyword --- It is required to be the first keyword in the primary header of all FITS file. The value field shall contain a logical constant with the value T if the file conforms to this standard. This keyword is mandatory for the primary header and is not permitted in extension headers. A value of F signifies that the file does not conform to this standard.

BITPIX Keyword --- The value field shall contain an integer, and it shall specify the number of bits that represent a data value. A value of -32 represents IEEE single precision floating point.

NAXIS Keyword --- The value field shall contain a non-negative integer no greater than 999, representing the number of axes in the associated data array. A value of zero signifies that no data follow the header in the HDU.

EXTEND Keyword --- The value field shall contain a logical value indicating whether the FITS file is allowed to contain conforming extensions following the primary HDU. This keyword may only appear in the primary header and must not appear in an extension header. If the value field is T then there may be conforming extensions in the FITS file following the primary HDU. This keyword is only advisory, so its presence with a value T does not require that the FITS file contains extensions, nor does the absence of this keyword necessarily imply that the file does not contain extensions.

2.3.2 File Information Keywords

FILENAME= 'med-58120-NGC228101_sp08-178.fits' /
OBSID   =            624608178 / Unique number ID of this spectrum
AUTHOR  = 'LAMOST Pipeline'    / Who compiled the information
DATA_V  = 'LAMOST DR10'   / Data release version
N_EXTEN =                    9 / The extension number
EXTNAME = 'Information'        / The extension name
ORIGIN  = 'NAOC-LAMOST'        / Organization responsible for creating this file
DATE    = '2020-02-19T12:54:18' / Time when this HDU is created (UTC)

FILENAME Keyword --- The value field shall contain a character string giving the name of this FITS file. Take the “med-58120-NGC228101_sp08-178.fits” as an example. “58120” is the local modified Julian day, “NGC228101_sp08” is the plan ID, “sp08” is the spectrograph ID, and “178” is the Fiber ID.

OBSID Keyword --- The value field shall be a non-negative integer giving the number ID of this spectrum.

AUTHOR Keyword --- This keyword contains a string constant “LAMOST Pipline”, which represents the author who produce this file.

DATA_V Keyword --- This keyword contains a string constant, which represents the data release version.

N_EXTEN Keyword --- The value field shall contain an integer giving the extension number of a FITS file.

EXTNAME Keyword --- This keyword contains a character string to be used to distinguish among different extensions of the same type in a FITS file. Within this context, the primary array should be considered as equivalent to an IMAGE extension.

ORIGIN Keyword --- This ORIGIN keyword contains a string constant “NAOC-LAMOST”, which indicates the Organization responsible for this FITS file. “NAOC” represents the abbreviation of National Astronomical Observatories, Chinese Academy of Sciences.

DATE Keyword --- The value field shall contain a character string giving the UTC time when this FITS file is created.

2.3.3 Telescope Parameter Keywords

TELESCOP= 'LAMOST  '           / GuoShouJing Telescope
LONGITUD=               117.58 / [deg] Longitude of site
LATITUDE=                40.39 / [deg] Latitude of site
FOCUS   =                19964 / [mm] Telescope focus
CAMPRO  = 'NEWCAM  '           / Camera program name
CAMVER  = 'v2.0    '           / Camera program version

TELESCOP Keyword --- This keyword contains a string constant “LAMOST” giving the name of our telescope.

LONGITUD Keyword --- The keyword contains a floating-point constant, which provide the longitude of Xinglong station where LAMOST is mounted on.

LATITUDE Keyword --- The keyword contains a floating-point constant, which provide the latitude of Xinglong station.

FOCUS Keyword --- The FOCUS keyword gives the telescope focus, and its unit is millimeter.

CAMPRO Keyword --- The value field contain a string constant “NEWCAM”, which shows the name of camera.

CAMVER Keyword --- The value field contain a character string, which gives the present camera program version.

2.3.4 Observation Parameter Keywords

DATE -OBS= '2018-01-01T15:21:00' / The observation median UTC
DATE-BEG= '2018-01-01T23:03:26.0' / The observation start local time
DATE-END= '2018-01-01T23:40:15.0' / The observation end local time
LMJD    =                58120 / Local Modified Julian Day
MJD     =                58119 / Modified Julian Day
PLANID  = 'NGC228101'          / Plan ID in use
RA      =           103.398334 / [deg] Right ascension of object
DEC     =            40.626064 / [deg] Declination of object
RA_OBS  =           103.398334 / [deg] Right ascension during observing
DEC_OBS =            40.626064 / [deg] Declination during observing
OFFSET  =                    F / Whether there's a offset during observing
OFFSET_V=                 0.00 / Offset value in arcsecond
GL      =           175.724039 / [deg] Galactic longitude of object
GB      =            17.653158 / [deg] Galactic latitude of object
DESIG   = 'LAMOST J065335.60+403733.8' / Designation of LAMOST target
FIBERID =                  178 / Fiber ID of Object
CELL_ID = 'F2217   '           / Fiber Unit ID on the focal plane
X_VALUE =             -191.336 / [mm] X coordinate of object on the focal plane
Y_VALUE =              398.645 / [mm] Y coordinate of object on the focal plane
OBJNAME = 'UCAC4_654-044946'   / Name of object
OBJTYPE = 'STAR    '           / Object type from input catalog
TSOURCE = 'LAMOST  '           / Name of input catalog
TCOMMENT= '        '           / Target information
TFROM   = '        '           / Target catalog
FIB_TYPE= 'Obj     '           / Fiber type of object
FIB_MASK=                    0 / Bitmask of warning values, 0 means good
MAG_PS_G=                13.47 / [mag] Magnitude of object
MAG_PS_R=                12.95 / [mag] Magnitude of object
MAG_PS_I=                12.75 / [mag] Magnitude of object
MAG_PS_Z=                99.00 / [mag] Magnitude of object
MAG_PS_Y=                99.00 / [mag] Magnitude of object
OBS_TYPE= 'OBJ     '           / The type of target (OBJ, FLAT, ARC or BIAS)
OBSCOMM = 'Science '           / Science or Test
RADECSYS= 'FK5     '           / Equatorial coordinate system
EQUINOX =              2000.00 / Equinox in years
SKYLIST = 'skylines.dat'       / Sky emission line list
NEXP_B  =                    3 / Number of valid blue exposures
COMBIN_B=                    T / Whether the combined data of B band exists
NEXP_R  =                    3 / Number of valid red exposures
COMBIN_R=                    T / Whether the combined data of R band exists
SCAMEAN =                41.53 / [ADU] Mean level of scatter light

DATE-OBS Keyword --- The value field shall contain a character string, which gives the median moment UTC of multiple exposures.

DATE-BEG Keyword --- The value field shall contain a character string giving the observation start Beijing Time.

DATE-END Keyword --- The value field shall contain a character string, which provide the observation end Beijing Time.

LMJD Keyword --- The value field shall a non-negative integer giving the local modified Julian day.

MJD Keyword --- The value field shall be a non-negative integer giving the modified Julian day.

PLANID Keyword --- The value field shall contain a character string providing the plan name of the target.

RA Keyword --- The value field shall contain a non-negative real floating-point number, which gives the right ascension of target from the input catalog.

DEC Keyword --- The value field shall contain a real floating-point number, which gives the declination of target from the input catalog.

RA_OBS Keyword --- The value field shall contain a non-negative real floating-point number, which gives the pointing right ascension of target during observation.

DEC_OBS Keyword --- The value field shall contain a non-negative real floating-point number, which gives the pointing declination of target during observation.

OFFSET Keyword --- The value field shall contain a boolean value (T or F), which indicates if there is a fiber-offset for the target. The fiber-offset usually applied for the very bright stars (r<11) to avoid CCD saturation.

OFFSET_V Keyword --- The value field shall contain a real floating-point number giving the offset value in unit of arcsec.

GL Keyword --- The value field shall contain a real floating-point number, which gives the galactic longitude of target.

GB Keyword --- The value field shall contain a real floating-point number, which gives the galactic latitude of target.

DESIG Keyword --- The value field shall contain a character string, which indicates the name of LAMOST target. Like the name of SDSS target, numbers after the character “J” and before “+” represents RA in unit of HMS, and numbers after the character “+” are DEC in unit of DMS.

FIBERID Keyword --- The value field shall contain a non-negative integer between 1 and 250, which shows the fiber ID and shall be used together with the spectrograph ID.

CELL_ID Keyword --- The value field shall contain a character string, which gives the fiber unit ID on the focal plane. LAMOST focal plane is divided into four quadrant named “EFGH” respectively, the first character of this keyword represents the quadrant number, the first two numbers after the first character is the row number in this quadrant, and the next two numbers is the column numbers.

X_VALUE and Y_VALUE Keywords --- The value field shall contain two real floating-point numbers, which give X and Y coordinates of target on the focal plane.

OBJNAME Keyword --- The value field shall contain character string, giving the name ID of object that determined by the RA, DEC and HTM method.

OBJTYPE Keyword --- The value field shall contain a character string giving the class of objects in input catalogs.

TSOURCE Keyword --- The value field shall contain a character string which shows the name of organization or person who submit input catalog.

TCOMMENT Keyword --- The value field shall contain a character string which shows the target ID from SDSS, UCAC4, Pan-STARRS and other catalogues.

TFROM Keyword --- The value field shall contain a character string which shows input catalog submitted by an organization or a person determined by the TSOURCE.

FIB_TYPE Keyword --- The value field shall contain a character string, giving the type of fiber assigned to this target. This keyword has six values, i.e., Obj, Sky, F-std, Unused, PosErr and Dead. Obj means the fiber is assigned to an object, including star, galaxy and so on. Sky indicates that the fiber is allocated to take skylight. F-std shows the fiber is used to take the light of a flux calibration standard star. Unused, PosErr and Dead mean the unused fiber, a wrong fiber position, or out of commission respectively.

FIB_MASK Keyword --- The value field shall contain an integer, which is used to show the problems of fibers. If you want to know the exact problem of a fiber, you should first convert the decimal value of “FIB_MASK” to a nine-bit binary number, which is shown in table 1. If the value of a bit is 1, it represents the fiber has associated problem, and the following table 2 lists the associated fiber problem of each bit. 

Table 1: Nine bits of the “FIB_MASK” field

9

8

7

6

5

4

3

2

1

 

Table 2: The fiber problems

Bit

Problem

Comment

1

NOALLOTTED

Fiber not allotted

2

BADTRACE

Bad trace from the routine TRACECENTER

3

BADFLAT

Low counts in flat field

4

BADARC

Bad arc solution

5

MANYBADPIXEL

>10% pixels are bad on CCD

6

SATURATED

>10% pixels are saturated

7

WHOPPER

Whopping fiber

8

NEARWHOPPER

Near a whopping fiber

9

BADSKYFIBER

Sky fiber shows extreme residuals

 

MAG_PS_G, MAG_PS_R, MAG_PS_I, MAG_PS_Z, and MAG_PS_Y Keywords --- The value field shall contain a real floating-point number between 0 and 100, giving the Pan-STARRS g/r/i/z/y band magnitudes. 

OBS_TYPE Keyword --- The value field shall contain a character string giving the type of observation targets, which include object, flat, bias and arc lamp.

OBSCOMM Keyword --- The value field shall contain a character string constant representing the observation purposes , which includes observations used for science researches and kinds of tests.

RADECSYS Keyword --- The value field shall contain a character string giving the equatorial coordinate system based on the J2000 position.

EQUINOX Keyword --- The value field shall contain a real floating-point number giving the standard epoch used at present.

SKYLIST Keyword --- The value field shall contain a character string giving the file name of sky emission line list, which is used in the process of sky subtraction.

NEXP_B and NEXP_R Keywords --- The value field of the two keywords shall contain two non-negative integers, which provide numbers of valid blue and red exposures respectively.

COMBIN_B and COMBIN_R Keywords --- The value field shall contain a boolean value (T or F), which indicates whether the coadded B or R band spectrum exists.

SCAMEAN Keyword --- The value field shall contain a real floating-point giving the mean level of scatter light, which is the average flux of regions where there is no fiber and is at the left and right edge of a two dimension spectra image.

2.3.5 Spectrograph Parameters Keywords

SPID    =                    8 / Spectrograph ID
SPRA    =           103.7905998 / [deg] Average RA of this spectrograph
SPDEC   =            41.0968508 / [deg] Average DEC of this spectrograph
SLIT_MOD= 'x2/3    '           / Slit mode, x1, x2/3 or x1/2

SPID Keyword --- The value field shall contain a non-negative integer numbers between 1 and 16, which provides the spectrograph ID.

SPRA and SPDEC Keywords --- The value field of these two keywords shall contain two real floating-point numbers, which are the averages of RA and DEC of all objects in each spectrograph.

SLIT_MOD Keyword --- The value field shall contain a character string of “x2/3”, which gives the slit mode and responds spectra resolution of 7500 respectively at 5163 Å (blue) and 6593 Å (red).   

2.3.6 Weather Condition Keywords

SEEING  =                 2.68 / [arcsec] Seeing during exposure
MOONPHA =                14.86 / [day] Moon phase for a 29.53 days period
TEMP_AIR=                -6.88 / [deg] Temperature outside dome
TEMP_FP =                -1.90 / [degree celsius] Temprature of the focalplane
DEWPOINT=               -22.54 / [deg]
DUST    = '        '           / Reservation
HUMIDITY=                27.43 /
WINDD   =               130.34 / [deg] Wind direction
WINDS   =                 0.32 / [m/s] Wind speed
SKYLEVEL= '        '           / Reservation

SEEING Keyword --- The value field shall contain a real floating-point number giving seeing during exposure, which is calculated by manually measuring the full width at half maximum of guide star image.

MOONPHA Keyword --- The value field shall contain a real floating-point number giving the moon phase.

TEMP_AIR Keyword --- The value field shall contain a real floating-point number giving the temperature outside dome, which is measured by automatic weather instrument. The unit “degree” represents centigrade degree.

TEMP_FP Keyword ---The value field shall contain a real floating-point number giving the temperature of focal plane, which is measured by automatic weather instrument. The unit “degree” represents centigrade degree.

DEWPOINT Keyword --- The value field shall contain a real floating-point number giving the dew-point temperature, which is also measured by the automatic weather instrument. The unit “degree” represents centigrade degree.

DUST Keyword --- The value of this keyword is temporarily empty at present, because the dust measuring instrument is now in debugging, and we will write this parameter into fits header when problems are resolved.

HUMIDITY Keyword --- The value field shall contain a real floating-point number between 0 and 1, which gives humidity in the air.

WINDD Keyword --- The value field shall contain a real floating-point number which records the instantaneous wind direction when start exposure, and the direction of north is the 0 degree wind direction.

WINDS Keyword --- The value field shall contain a real floating-point number which records the instantaneous wind speed when start exposure, and wind direction and speed are also measured also by the automatic weather instrument.

SKYLEVEL Keyword --- This keyword is NULL now, because the instrument is debugging.

2.3.7 Data Reduction Parameters Keywords

EXTRACT = 'aperture'           / Extraction method
SFLATTEN=                    T / Super flat has been applied
PCASKYSB=                    T / PCA sky-subtraction has been applied
NSKIES  =                   34 / Sky fiber number
SKYCHI2 =                  3.4 / Mean chi^2 of sky-subtraction
HELIO   =                    T / Heliocentric correction
HELIO_RV=             -0.07809 / [km/s] Heliocentric correction
VACUUM  =                    T / Wavelengths are in vacuum

EXTRACT Keyword --- The value field shall contain a character string, which indicates the method of spectrum extraction. In LAMOST spectra reduction pipeline, only the aperture method is applied to spectra extraction.

SFLATTEN Keyword --- The value of this keyword shall be boolean, which represents whether or not use the super flat. In LAMOST spectra reduction pipeline, super flat is used to make the fiber-to-fiber relative efficiency around 1.

PCASKYSB Keyword --- The value of this keyword shall be boolean, which represents whether or not use the PCA method to subtract sky light. In LAMOST spectra reduction pipeline, the PCA method is used to subtract sky light at the wavelength range larger than 7200 Å.

NSKIES Keyword --- The value field shall contain an integer, which shows the number of sky fiber in a spectrograph.

SKYCHI2 Keyword --- The value field shall contain a real floating-point, which gives the mean chi-square of sky-subtraction. In the process of LAMOST spectra reduction, super sky is obtained by spline fitting m sky spectra. And thus, the chi-square between the super sky and each sky spectra in an exposure, and the average chi-square of m sky spectra can also be able to obtain. Assuming n times exposures, there will be 2n average chi-square because of n blue spectra and n red spectra, and this keyword will be evaluated by calculating the mean value of these 2n average chi-squares.

HELIO Keyword --- The value of this keyword shall be boolean, which represents whether or not to perform the heliocentric correction.

HELIO_RV Keyword --- The value field shall contain a real floating-point, which gives the radial velocity used to carry out the heliocentric correction.

VACUUM Keyword --- The value of this keyword shall be boolean, which represents whether or not the LAMOST spectra is converted to vacuum wavelength.

2.4 Extention 1 and 2

If a LAMOST target has coadded B and R band spectra, the extension 1 and 2 provide the information of their coadded spectra, otherwise the two extension do not have the data array as the primary extension.

In this section, we only introduce extension 1 and 2 for targets which have the coadded spectra. Following sub-section 2.4.1 will introduce each keyword in the header file, and the data array will be presented in the sub-section 2.4.2.

2.4.1 Keywords

In this sub-section, we introduce each keyword in the header file of extension 1 and 2, and all keywords are shown as follows.

XTENSION= 'BINTABLE'           /Binary table written by MWRFITS v1.11b
BITPIX  =                    8 /Required value
NAXIS   =                    2 /Required value
NAXIS1  =                   16 /Number of bytes per row
NAXIS2  =                 3760 /Number of rows
PCOUNT  =                    0 /Normally 0 (no varying arrays)
GCOUNT  =                    1 /Required value
TFIELDS =                    5 /Number of columns in table
EXTNAME = 'COADD_B '           / The extension name
LMJMLIST= '83692743-83692756-83692770' / Local Modified Julian Minute list
DATE-OBS= '2018-01-01T15:21:00' / The observation median UTC
DATE-BEG= '2018-01-01T23:03:26.0' / The observation start local time
DATE-END= '2018-01-01T23:40:15.0' / The observation end local time
LAMPLIST= 'lampsc_med.dat'     / Arc lamp emission line list
SNR     =                36.93 / Signal to noise ratio
TTYPE1  = 'FLUX    '           /
TTYPE2  = 'IVAR    '           /
TTYPE3  = 'WAVELENGTH'           /
TTYPE4  = 'ANDMASK '           /
TTYPE5  = 'ORMASK  '           /
TTYPE6   = 'NORMALIZATION'         /
TFORM1  = 'E       '           /
TFORM2  = 'E       '           /
TFORM3  = 'E       '           /
TFORM4  = 'I       '           /
TFORM5  = 'I       '           /
TFORM6  = 'I       '           /

XTENSION Keyword --- The value field shall contain a character string giving the name of the extension type. This keyword is mandatory for an extension header and must not appear in the primary header.  

BITPIX Keyword --- The value field shall contain an integer, and it shall specify the number of bits that represent a data value. A value of -32 represents IEEE single precision floating point.

NAXIS Keyword --- The value field shall contain a non-negative integer no greater than 999, representing the number of axes in the associated data array. A value of zero signifies that no data follow the header in the HDU.

NAXIS1 and NAXIS2 Keywords --- The value field of these two indexed keywords shall contain a non-negative integer, representing the number of elements along axis n of a data array. NAXIS2 is the row number of extension 1, and NAXIS1 is the byte number of each row.

PCOUNT Keyword --- The value field shall contain an integer that shall be used in any way appropriate to define the data structure. In IMAGE and TABLE extensions this keyword must have the value 0; in BINTABLE extensions, it is used to specify the number of bytes that follow the main data table in the supplemental data area called the heap.

GCOUNT Keyword --- The value field shall contain an integer that shall be used in any way appropriate to define the data structure. This keyword must have the value 1 in the IMAGE, TABLE and BINTABLE standard extensions.

TFIELDS Keyword --- The value field shall contain a non-negative integer representing the number of fields in each row. The maximum permissible value is 999.

EXTNAME Keyword --- This keyword contains a character string to be used to distinguish among different extensions of the same type in A FITS file. Within this context, the primary array should be considered as equivalent to an IMAGE extension.

LMJMLIS0-(n-1) Keyword --- This keyword contains a character string to show local modified Julian Minutes (LMJM) of N exposures. For each LMJMLISi (i = 0,2,…n-1), it includes the LMJM of three exposures at most. If the number of exposures (N) is larger than three, then n can be obtained with the equation of n = floor(N / 3) + 1, where floor represents round down. When N is less than three, the only LMJMLIS0 keyword will be renamed as the “LMJMLIST”.

DATE-OBS Keyword --- The value field shall contain a character string, which gives the median moment UTC of multiple exposures.

DATE-BEG Keyword --- The value field shall contain a character string giving the observation start Beijing Time.

DATE-END Keyword --- The value field shall contain a character string, which provide the observation end Beijing Time.

LAMPLIST Keyword --- The value field shall contain a character string giving the file name of arc lamp emission line list, which is used in the process of wavelength calibration.

SNR Keyword --- The value field for this keyword shall contain a real floating-point, which is the median of S/Ns of all pixels. The S/N of each pixel is calculated by the equation of flux * (inverse variance) ^ 0.5.

TTYPE1-n Keywords --- These keywords are of string type, providing the names of the ith (i = 1, 2, 3, ... n) column in the extension data array.

TFORM1-n Keywords --- These keywords are string types, used to describe the data type of the ith (i = 1, 2, 3, ... n) column in the extension data array.

2.4.2 Data Array

The data array of extension 1 and 2 have five columns, and table 3 explains the data in each column.

Table 3: Data array of extension 1 and 2

Column Number

Data

Type

5

Ormask

float

4

Andmask

float

3

WaveLength

float

2

Inverse Variance

float

1

Flux

float

 

The data array of extension 1 and 2 in LAMOST MR FITS file is shown in table 3. The first column is flux, the second column stores the “inverse variance” of the uncertainties (one over sigma-squared), which can be used to estimate S/N of each pixel (flux * (inverse variance) ^ 0.5), and the third column stores wavelength in unit of Å. The “andmask” information in fourth column is a decimal integer determined by a six-bit binary number shown in table 4, which represents six situations respectively listed in table 5, and the associated bit of “andmask” will be set to 1 if the case always appears in each exposure. Like the “andmask”, the “ormask” information in fifth column is also a decimal integer determined by a six-bit binary number. The difference is that each bit of “ormask” will be set to 1 if the related case happens in any exposure.

Table 4: Six bits of “Andmask” and “Ormask”

6

5

4

3

2

1

 

Table 5: The significance of six bits of “Andmask” and “Ormask”

Bit

Keyword

Comments

1

BADCCD

bad pixel on CCD

2

BADPROFILE

bad profile in extraction

3

NOSKY

no sky information at this wavelength

4

BRIGHTSKY

sky level too high

5

BADCENTER

fiber trace out of the CCD

6

NODATA

no good data

 

If you want to check which case in table 5 has happened in the spectrum reduction process, you can firstly convert the decimal “Andmask” or “Ormask” to a six-bit binary number. Then, a case must has happened in each exposure if associated bit is 1 in binary “Andmask”, and a case must has happened at least one time if associated bit is 1 in binary “Ormask”.

2.5 Extension 3 to (N-1)

In this section, we introduce the single exposure extensions. In the title of this section, N is the total number of extensions which can be obtained from the keyword “N_EXTEN” in the header of primary extension. Assuming the target has n B band and n R band single exposure spectra, N is equal to 2n + 3. 

In the following sub-section, we introduce each keyword in the header file, and the structure of data array.

2.5.1 Keywords

In this sub-section, all keywords in the header are shown as follows, and they are explained in detail.

XTENSION= 'BINTABLE'           /Binary table written by MWRFITS v1.11b
BITPIX  =                    8 /Required value
NAXIS   =                    2 /Required value
NAXIS1  =                   14 /Number of bytes per row
NAXIS2  =                 4136 /Number of rows
PCOUNT  =                    0 /Normally 0 (no varying arrays)
GCOUNT  =                    1 /Required value
TFIELDS =                    4 /Number of columns in table
EXTNAME = 'R-83692756'         / The extension name
DATE-OBS= '2018-01-01T15:21:00' / The observation median UTC
DATE-BEG= '2018-01-01T23:16:48.0' / The observation start local time
DATE-END= '2018-01-01T23:26:48.0' / The observation end local time
LMJM    = '83692756'           / Local Modified Julian Minute
EXPTIME =                  600 / [s] Exposure duration time
SNR     =                28.58 / Signal to noise ratio
LAMPLIST= 'lampsc_med.dat'     / Arc lamp emission line list
TTYPE1  = 'FLUX    '           /
TTYPE2  = 'IVAR    '           /
TTYPE3  = 'WAVELENGTH'           /
TTYPE4  = 'PIXMASK '           /
TTYPE5  = 'NORMALIZATION'      /
TFORM1  = 'E       '           /
TFORM2  = 'E       '           /
TFORM3  = 'E       '           /
TFORM4  = 'I       '           /
TFORM5  = 'E       '           /

XTENSION Keyword --- The value field shall contain a character string giving the name of the extension type. This keyword is mandatory for an extension header and must not appear in the primary header.  

BITPIX Keyword --- The value field shall contain an integer, and it shall specify the number of bits that represent a data value. A value of -32 represents IEEE single precision floating point.

NAXIS Keyword --- The value field shall contain a non-negative integer no greater than 999, representing the number of axes in the associated data array. A value of zero signifies that no data follow the header in the HDU.

NAXIS1 and NAXIS2 Keywords --- The value field of these two indexed keywords shall contain a non-negative integer, representing the number of elements along axis n of a data array. NAXIS2 is the row number of extension 1, and NAXIS1 is the byte number of each row.

PCOUNT Keyword --- The value field shall contain an integer that shall be used in any way appropriate to define the data structure. In IMAGE and TABLE extensions this keyword must have the value 0; in BINTABLE extensions, it is used to specify the number of bytes that follow the main data table in the supplemental data area called the heap.

GCOUNT Keyword --- The value field shall contain an integer that shall be used in any way appropriate to define the data structure. This keyword must have the value 1 in the IMAGE, TABLE and BINTABLE standard extensions.

TFIELDS Keyword --- The value field shall contain a non-negative integer representing the number of fields in each row. The maximum permissible value is 999.

EXTNAME Keyword --- This keyword contains a character string to be used to distinguish among different extensions of the same type in a FITS file. Within this context, the primary array should be considered as equivalent to an IMAGE extension.

DATE-OBS Keyword --- The value field shall contain a character string, which gives the median moment UTC of multiple exposures.

DATE-BEG Keyword --- The value field shall contain a character string giving the observation start Beijing Time.

DATE-END Keyword --- The value field shall contain a character string, which provide the observation end Beijing Time.

LMJM Keyword --- This keyword contains a character string to show the local modified Julian Minute at the start of exposure. 

EXPTIME Keyword --- The value field for this keyword shall contain a real floating-point, which gives the exposure duration time.

SNR Keyword --- The value field for this keyword shall contain a real floating-point, which is the median of S/Ns of all pixels. The S/N of each pixel is calculated by the equation of flux * (inverse variance) ^ 0.5.

LAMPLIST Keyword --- The value field shall contain a character string giving the file name of arc lamp emission line list, which is used in the process of wavelength calibration.

TTYPE1-n Keywords --- These keywords are of string type, providing the names of the ith (i = 1, 2, 3, ... n) column in the extension data array.

TFORM1-n Keywords --- These keywords are string types, used to describe the data type of the ith (i = 1, 2, 3, ... n) column in the extension data array.

2.5.2 Data Array

In this sub-section, we describe the data array of single exposure extensions, and it is shown in table 6. Like the data array of extension 1 and 2, they are flux, inverse variance, and wavelength in unit of Å from the first to third column. The different is that the data array of single exposure only has four columns, and the fourth column is the “Pixmask”, which is a decimal integer determined by a six-bit binary number. As the “Andmask” and “Ormask”, each bit of the “Pixmask” represents each issues of each pixel listed in table 5, and it will be 1 if the problem happens.  

Table 6: Data array

Column Number

Data

Type

4

Pixmask

float

3

WaveLength

float

2

Inverse Variance

float

1

Flux

float

 

Section 3. Catalog

In this section, we introduce five LAMOST MRS catalogs, which can be available from the website of http://www.lamost.org/dr10/V2.0/catalogue, and they are the LAMOST MRS General Catalog, the LAMOST MRS Parameter Catalog, the LAMOST MRS Multiple Epoch Catalog, the LAMOST MRS Observed Plate Information Catalog, and the LAMOST MRS Input Catalog, respectively. 

This time, targets with angular distances to the moon larger than 10 degrees were not observed, and there are three fields related to the angular distances to the moon in the LAMOST MRS General Catalog and the LAMOST MRS Parameter Catalog, which are “moon_angle”, “lunardate”, and “moon_flg” respectively. “moon_angle” represents the angular distance of each target to the moon, and “moon_flg” is a flag for it. “moon_flg” has two values of 0 and 1, which represent the range of angular distance. If “moon_flg” equals to 1, it indicates that angular distance is in the range of [10 degree, 30 degree], and it represents that the angular distance is larger than 30 degree when “moon_flg” equals to 0. In addition, “lunardate” is the date of Chinese lunar calendar, which represents the moon phase, and it has values from 1 to 30.

LAMOST targets were cross-matched with Gaia DR3, their Gaia source identifiers, i.e., the “source_id” fields, Gaia G, BP and RP magnitudes, i.e., the “phot_g_mean_mag”, “phot_bp_mean_mag”, and “phot_rp_mean_mag” fields, were included in the LAMOST MRS General Catalog and the LAMOST MRS Parameter Catalog, and they were marked as “gaia_source_id”, “gaia_g_mean_mag”, “gaia_bp_mean_mag”, and “gaia_rp_mean_mag”, respectively.

The following table 7, 8, 9, 10, and 11 separately show all fields of the four catalogs, and provide clear comment for each field. Most fields of these tables are explained in detail in sub-section 2.3, and we only introduce the fields which are not introduced in previous sections. 
 

3.1 LAMOST MRS General Catalog

In this sub-section, we present the LAMOST MRS General Catalog, which includes 52 parameters for 31,043,138 single exposure spectra and 8,333,131 coadded spectra in this table. All fields of this catalog are listed in table 7, most of them are explained in section 2.3 in detail, and we only introduce fields not mentioned above. 

In this table and the following LAMOST MRS Parameter catalog, there are two unique spectrum IDs, and they are “mobsid” and “obsid”, respectively. The “mobsid” field is the unique ID for each medium-resolution spectrum, and the “obsid” field is the unique spectrum ID for each observation of each target.

We artificially add offsets to the equatorial coordinates of input catalog to prevent saturation for a fraction of luminous stars during observation. Thus, four fields were added in this and other two catalogs (the LAMOST MRS Parameter Catalog and LAMOST MRS Input Catalog), and they are “ra_obs”, “dec_obs”, “offsets” and “offsets_v” respectively. The “ra_obs” and “dec_obs” are fiber pointing right ascension and declination during observation, and the “ra” and “dec” are the equatorial coordinates from the input catalog. The “offsets” represents whether there is a fiber offset during observation, and the “offsets_v” gives the offset value of equatorial coordinator in the input catalog if the “offsets” field is true. Note that, “offsets” and “offsets_v” in catalogs are the same as “offset” and “offset_v” in FITS header. Since “offset” is a commonly used database keyword, it should be avoided to use in catalogs.

The catalog provides eight radial velocity measurements and errors, which are also in the following LAMOST MRS Parameter catalog, and they are “rv_b0”, “rv_b1”, “rv_r0”, “rv_r1”, “rv_br0”, “rv_br1”, “rv_lasp0”, “rv_lasp1”, “rv_b0_err”, “rv_b1_err”, “rv_r0_err”, “rv_r1_err”, “rv_br0_err”, “rv_br1_err”, “rv_lasp0_err”, and “rv_lasp1_err”, respectively. The “rv_b0”, “rv_r0”, and “rv_br0” velocities were determined by the cross-correlation method, which used 483 selected KURUCZ synthetic spectra as the templates, and their difference lies in different band of spectra were used. The “rv_b0” and “rv_r0” were estimated with the B and R band spectra, respectively, and the “rv_br0” was determined with both B and R band spectra after continuum removal. The “rv_b1”, “rv_r1”, and “rv_br1” velocities are calibrated velocities of “rv_b0”, “rv_r0”, and “rv_br0”, which were calibrated by the radial velocity standard stars provided in Huang, Y. et al (2018)[2]. It should be noted that “rv_b1”, “rv_r1”, and “rv_br1” have only corrected the systematic errors between spectrographs, which do not include systematic errors between fibers and exposures, and the detailed correction method was introduced in Wang, R. et al (2019)[3]. The “rv_lasp0” velocity was estimated by the LASP, and “rv_lasp1” is the calibrated velocity of “rv_lasp0”. 

The radial velocity uncertainty is affected mainly by two factors, i.e., the S/N and the best-matched chi-square. Using a sample of stars subtracting variable stars and having multiple observations, the radial velocity precision (RVP) for each observation and the relationship between the RVP and S/N were determined. Besides, the function relationship of the best-matched chi-square and S/N can also be obtained with another sample of stars. The uncertainties of “rv_b0”, “rv_r0” and “rv_br0” are “rv_b0_err”, “rv_r0_err”, and “rv_br0_err”, respectively, and they are estimated with the best-matched chi-square, S/N, and the above two relationships. The uncertainties of calibrated “rv_b1”, “rv_r1”, and “rv_br1” velocities are “rv_b1_err”, “rv_r1_err”, and “rv_br1_err”, respectively, and they are determined by the error propagation method. In addition, “rv_lasp0_err”, and “rv_lasp1_err” are uncertainties of “rv_lasp0” and “rv_lasp1”, and they were estimated by the same method mentioned above. 

There are three radial velocity flags in this table, and they are “rv_b_flag”, “rv_r_flag”, “rv_br_flag”, respectively, which represents possible problems of radial velocities. Each of the three flags has four values, and they “0”, “1”, “2”, and “3”, which represent no exceptions, too many bad pixels (there are more than a third of bad pixels in a spectrum), the absolute value of radial velocity larger than 450 km/s, and low similarity with the best-matched template, respectively.

There are also five flags in this table, and they are “band”, “coadd”, “fibermask”, “bad_b”, and “bad_r”, respectively. The “band” field has two values of B and R, which represents the B and R band spectra, respectively. The “coadd” field can be used to determine whether this is a coadd spectrum, and it has two values of 0 (a single exposure spectrum) and 1 (a coadd spectrum). The “fibermask” field is the same as the “FIB_MASK ” field in the primary extension, which has already detailedly described in subsection 2.3.4. The last two fields of “bad_b” and “bad_r” can be used to show whether each B and R band spectra are problematic, each of them has two values of “0” (the B or R band spectrum has no problem) and “1” (the B or R band spectrum is problematic).

The LAMOST Medium-Resolution Survey was divided into a few different sub-surveys, the “subproject” field provides the name of each sub-project, which is written as “MRS_TD/NT_X”. “MRS” means the LAMOST Medium-Resolution Spectroscopic Survey, and “TD” and “NT” are observation modes, i.e., time-domain and non time-domain. “X” is the sub-project name, and it has values of “K”, “B”, “M”, “T”, “S”, “C”, “N”, and “H”, which represents “the Kepler region survey”, “the binary survey”, “the Milky Way survey”, “the TESS follow-up survey”, “the star forming region survey”, “the open cluster survey”, “the Galactic nebulae survey”, and “Four K2 binary test fields”, respectively.

Here, we provide two formats of the LAMOST MRS General Catalog to download, which include a FITS table and a CSV table, and they can be available from http://www.lamost.org/dr10/V2.0/catalogue.

Table 7: LAMOST MRS General Catalog

Field (unit)

Type

Comment

mobsid

long integer

Unique ID for each medium-resolution spectrum in each exposure

obsid

long integer

Unique spectrum ID for each observation of each target

uid

char

Unique source identifier calculated with the “ura” and “udec” in table 9

gp_id

char

For each LAMOST source, the equatorial coordinates (“ura” and “udec” in table 9) used to calculate “uid” were from which survey ((Pan-STARRS, Gaia or LAMOST), “gp_id” gives the corresponding source identifier in that survey.

designation

char

Target designation

obsdate

char

Target observation date

lmjd

char

Local modified Julian day

mjd

char

Modified Julian day

planid

char

Plan name

spid

integer

Spectrograph ID

fiberid

integer

Fiber ID

lmjm

char

Local modified Julian minute

band

char

Having two values of B and R, which represent B and R band spectra

ra_obs (degree)

float

Fiber pointing right ascension

dec_obs (degree)

float

Fiber pointing declination

snr

float

The median value of all pixel S/Ns in B band spectrum or R band

gaia_source_id

char

The "source_id" field of Gaia DR3 catalog

gaia_g_mean_mag (mag)

float

The "phot_g_mean_mag" field of Gaia DR3 catalog

gaia_bp_mean_mag (mag)

float

The "phot_bp_mean_mag" field of Gaia DR3 catalog

gaia_rp_mean_mag (mag)

float

The "phot_rp_mean_mag" field of Gaia DR3 catalog

fibertype

char

Fiber type of target

[Obj, Sky, F-std, Unused, PosErr, Dead]

offsets

bool

Whether there is a fiber offset during observation

offsets_v (arcsec)

float

If the “offsets” field is true, “offsets_v” gives the offset distance from the target”s coordinator in input catalog

ra (degree)

float

Right ascension from input catalog

dec (degree)

float

Declination from input catalog

rv_b0 (km/s)

float

Radial velocity of B band spectra measured with 483 selected KURUCZ synthetic templates

rv_b0_err (km/s)

float

Uncertainty of rv_b0 measured by the method LASP used

rv_b1 (km/s)

float

Radial velocity after zero-point correction of rv_b0

rv_b1_err (km/s)

float

Uncertainty of rv_b1 measured by the error propagation

rv_b_flag (km/s)

integer

Radial velocity flag for B band spectra

rv_r0 (km/s)

float

Radial velocity of R band spectra measured with 483 selected KURUCZ synthetic templates

rv_r0_err (km/s)

float

Uncertainty of rv_r0 measured by the method LASP used

rv_r1 (km/s)

float

Radial velocity after zero-point correction of rv_r0

rv_r1_err (km/s)

float

Uncertainty of rv_r1 measured by the error propagation

rv_r_flag

integer

Radial velocity flag for R band spectra

rv_br0 (km/s)

float

Radial velocity of B and R band spectra measured with 483 selected KURUCZ synthetic templates

rv_br0_err (km/s)

float

Uncertainty of rv_br0 measured by the method LASP used

rv_br1 (km/s)

float

Radial velocity after zero-point correction of rv_br0

rv_br1_err (km/s)

float

Uncertainty of rv_br1 measured by the error propagation

rv_br_flag (km/s)

integer

Radial velocity flag for B and R band spectra

rv_lasp0 (km/s)

float

Radial velocity measured by the LASP

rv_lasp0_err (km/s)

float

Uncertainty of rv_lasp0 also given by the LASP

rv_lasp1 (km/s)

float

Radial velocity after zero-point correction of rv_lasp0

rv_lasp1_err (km/s)

float

Uncertainty of rv_lasp1 measured by the error propagation

coadd

bool

A flag to show whether it is a coadd spectrum

fibermask

integer

Possible fiber problems

bad_b

bool

A flag to show whether the B band spectra is problematic

bad_r

bool

A flag to show whether the R band spectra is problematic

moon_angle (degree)

float

The angular distance of each target to the moon

lunardate

integer

The date of Chinese lunar calendar, which represents the moon phase, and its value is from 1 to 30.

moon_flg

bool

This is a flag for “moon_angle”, and it has two values of 0 and 1, which represent the range of angular distance. If “moon_flg” equals to 1, it indicates that angular distance is in the range of [10 degree, 30 degree], and it represents that the angular distance is larger than 30 degree when “moon_flg” equals to 0.

subproject

char

The sub-project names of LAMOST Medium-Resolution Spectroscopic Survey


3.2 LAMOST MRS Parameter Catalog

In this sub-section, we present the LAMOST MRS Parameter Catalog. In this table, atmospheric parameters and their uncertainties estimated by the LASP were released. For stars with effective temperatures in the range of [4500 K, 8500 K] or with effective temperatures in the range of [4000 K, 4500 K] and surface gravities less than 3.5 dex, blue coadd spectra were used, and red coadd spectra were adopted for stars with effective temperatures in the range of [3300 K, 4000 K] or with effective temperatures in the range of [4000 K, 4500 K] and surface gravities larger than or equal to 3.5 dex. Note that, no matter blue or red band spectra were used here, their signal to noise ratios should be larger than 10. Thus, we published atmospheric parameters for 2,066,618 blue coadd spectra, and for 96,320 red coadd spectra, respectively. In addition, alpha element abundances, atmospheric parameters, and 13 element abundances were also estimated by the convolutional neural network (CNN) method for these spectra, and they were also published in this catalog.

Table 8 lists all fields of this catalog, and fields before the “teff_lasp” have been introduced in subsection 3.1. The terms "teff_lasp", "logg_lasp", "feh_lasp", "vsini_lasp", "teff_lasp_err", "logg_lasp_err", "feh_lasp_err", and "vsini_lasp_err" correspond to effective temperature, surface gravity, metallicity, projected rotational velocity, and their errors as provided by LASP. Initially, effective temperature, surface gravity, and metallicity were measured using ELODIE template spectra. Based on these parameters, the projected rotational velocity was further measured using PHOENIX templates[4]. Note that, the uncertainty estimation methods of atmospheric parameters and projected rotation velocity given by the LASP are similar as the method of radial velocity uncertainties mentioned in subsection 3.1. In addition, the fields of “alpha_m_lasp” and “alpha_m_lasp_err” are alpha element abundance and the uncertainty given by the LASP, respectively. Different from above fields, the “alpha_m_lasp” field was estimated by the method of template matching based on the MARCS synthetic spectra, and the “alpha_m_lasp_err” is the uncertainty of “alpha_m_lasp”, which was estimated by the same method used by “teff_lasp_err”, “logg_lasp_err”, “feh_lasp_err”, and “vsini_lasp_err”.

The fields of “rv_b0”, “rv_b1”, “rv_r0”, “rv_r1”, “rv_br0”, “rv_br1”, “rv_lasp0”, “rv_lasp1”, “rv_b0_err”, “rv_b1_err”, “rv_r0_err”, “rv_r1_err”, “rv_br0_err”, “rv_br1_err”, “rv_lasp0_err”, “rv_lasp1_err”, “rv_b_flag”, “rv_r_flag”, “rv_br_flag”, “coadd”, and “fibermask” are also in the LAMOST MRS General Catalog of subsection 3.1, thus they are not introduced again here.

The fields of “alpha_m_cnn”, “m_h_cnn”，“teff_cnn”, “logg_cnn”, “feh_cnn”, “c_fe ”, “n_fe ”, “o_fe ”, “mg_fe ”, “al_fe ”, “si_fe ”, “s_fe ”, “ca_fe ”, “ti_fe ”, “cr_fe ”, “ni_fe ”, and “cu_fe ” are alpha element abundances, metallicity, effective temperature, surface gravity, and 13 element abundances, which were estimated by the label-transfer method based on a convolutional neural network (CNN) with both B and R band spectra after continuum removal , and the labels of the training samples were employed from APOGEE. Note, the uncertainties of these fields were not published in this data release, and the results obtained by the CNN method are only statistically significant.

Here, we provide two formats of the LAMOST MRS Parameter Catalog to download, which include a FITS table and a CSV table, and they can be available from http://www.lamost.org/dr10/V2.0/catalogue.

Table 8: LAMOST MRS Parameter Catalog

Field (unit)

Type

Comment

mobsid

long integer

Unique ID for each medium-resolution spectrum in each exposure

obsid

long integer

Unique spectrum ID for each observation of each target

uid

char

Unique source identifier calculated with the “ura” and “udec” in table 9

gp_id

char

For each LAMOST source, the equatorial coordinates (“ura” and “udec” in table 9) used to calculate “uid” were from which survey ((Pan-STARRS, Gaia or LAMOST), “gp_id” gives the corresponding source identifier in that survey.

designation

char

Target designation

obsdate

char

Target observation date

lmjd

char

Local modified Julian day

mjd

char

Modified Julian day

planid

char

Plan name

spid

integer

Spectrograph ID

fiberid

integer

Fiber ID

lmjm

char

Local modified Julian minute

band

char

Having two values of B and R, which represent B and R band spectra

ra_obs (degree)

float

Fiber pointing right ascension

dec_obs (degree)

float

Fiber pointing declination

snr

float

The median value of all pixel S/Ns in B band spectrum or R band

gaia_source_id

char

The "source_id" field of Gaia DR3 catalog

gaia_g_mean_mag (mag)

float

The "phot_g_mean_mag" field of Gaia DR3 catalog

gaia_bp_mean_mag (mag)

float

The "phot_bp_mean_mag" field of Gaia DR3 catalog

gaia_rp_mean_mag (mag)

float

The "phot_rp_mean_mag" field of Gaia DR3 catalog

fibertype

char

Fiber type of target

[Obj, Sky, F-std, Unused, PosErr, Dead]

offsets

bool

Whether there is a fiber offset during observation

offsets_v (arcsec)

float

If the “offsets” field is true, “offsets_v” gives the offset distance from the target”s coordinator in input catalog

ra (degree)

float

Right ascension from input catalog

dec (degree)

float

Declination from input catalog

teff_lasp (K)

float

Effective temperature given by the LASP

teff_lasp_err (K)

float

Effective temperature uncertainty given by the LASP

logg_lasp (dex)

float

Surface gravity given by the LASP

logg_lasp_err (dex)

float

Surface gravity uncertainty given by the LASP

feh_lasp (dex)

float

Metallicity given by the LASP

feh_lasp_err (dex)

float

Metallicity uncertainty given by the LASP

vsini_lasp

float

Projected rotation velocity given by the LASP

vsini_lasp_err

float

Uncertainty of vsini_el given by the LASP

rv_b0 (km/s)

float

Radial velocity of B band spectra measured with 483 selected KURUCZ synthetic templates

rv_b0_err (km/s)

float

Uncertainty of rv_b0 measured by the method LASP used

rv_b1 (km/s)

float

Radial velocity after zero-point correction of rv_b0

rv_b1_err (km/s)

float

Uncertainty of rv_b1 measured by the error propagation

rv_b_flag

integer

Radial velocity flag for B band spectra

rv_r0 (km/s)

float

Radial velocity of R band spectra measured with 483 selected KURUCZ synthetic templates

rv_r0_err (km/s)

float

Uncertainty of rv_r0 measured by the method LASP used

rv_r1 (km/s)

float

Radial velocity after zero-point correction of rv_r0

rv_r1_err (km/s)

float

Uncertainty of rv_r measured by the error propagation

rv_r_flag

integer

Radial velocity flag for R band spectra

rv_br0 (km/s)

float

Radial velocity of B + R spectra measured with 483 selected KURUCZ synthetic templates

rv_br0_err (km/s)

float

Uncertainty of rv_br0 measured by the method LASP used

rv_br1 (km/s)

float

Radial velocity after zero-point correction of rv_br0

rv_br1_err (km/s)

float

Uncertainty of rv_br1 measured by the error propagation

rv_br_flag (km/s)

integer

Radial velocity flag for B + R spectra

rv_lasp0 (km/s)

float

Radial velocity measured by the LASP

rv_lasp0_err (km/s)

float

Uncertainty of rv_lasp0 also given by the LASP

rv_lasp1 (km/s)

float

Radial velocity after zero-point correction of rv_lasp0

rv_lasp1_err (km/s)

float

Uncertainty of rv_lasp1 measured by the error propagation

coadd

bool

A flag to show whether it is a coadd spectrum

fibermask

integer

Possible fiber problems

alpha_m_cnn (dex)

float

Alpha element abundance estimated by the CNN method

m_h_cnn (dex)

float

Metallicity estimated by the CNN method

teff_cnn (K)

float

Effective temperature estimated by the CNN method

logg_cnn (dex)

float

Surface gravity estimated by the CNN method

feh_cnn (dex)

float

Fe abundance estimated by the CNN method

c_fe (dex)

float

Individual element abundance of [C/Fe] estimated by the CNN method

n_fe (dex)

float

Individual element abundance of [N/Fe] estimated by the CNN method

o_fe (dex)

float

Individual element abundance of [O/Fe] estimated by the CNN method

mg_fe (dex)

float

Individual element abundance of [Mg/Fe] estimated by the CNN method

al_fe (dex)

float

Individual element abundance of [Al/Fe] estimated by the CNN method

si_fe (dex)

float

Individual element abundance of [Si/Fe] estimated by the CNN method

s_fe (dex)

float

Individual element abundance of [S/Fe] estimated by the CNN method

ca_fe (dex)

float

Individual element abundance of [Ca/Fe] estimated by the CNN method

ti_fe (dex)

float

Individual element abundance of [Ti/Fe] estimated by the CNN method

cr_fe (dex)

float

Individual element abundance of [Cr/Fe] estimated by the CNN method

ni_fe (dex)

float

Individual element abundance of [Ni/Fe] estimated by the CNN method

cu_fe (dex)

float

Individual element abundance of [Cu/Fe] estimated by the CNN method

alpha_m_lasp (dex)

float

Alpha element abundance estimated by the LASP

alpha_m_lasp_err (dex)

float

The uncertainty of alpha_m_lasp

moon_angle (degree)

float

The angular distance of each target to the moon

lunardate

integer

The date of Chinese lunar calendar, which represents the moon phase, and its value is from 1 to 30.

moon_flg

bool

This is a flag for “moon_angle”, and it has two values of 0 and 1, which represent the range of angular distance. If "moon_flg" equals to 1, it indicates that angular distance is in the range of [10 degree, 30 degree], and it represents that the angular distance is larger than 30 degree when “moon_flg” equals to 0.

 

3.3 LAMOST MRS Multiple Epoch Catalog

In this sub-section, we introdu,ce the LAMOST MRS Multiple Epoch Catalog, and each row of this catalog represents a source with multiple observations. There are in total of 572,020 targets in this catalog, and there are 18 parameters provided for each source. The equator coordinates used to calculate the source identifier were mainly from the Gaia or Pan-STARRS survey. For a few sources without equator coordinates of Gaia or Pan-STARRS, the source identifiers were estimated with the equator coordinates in LAMOST input catalog.

In this catalog, “uid” is the unique LAMOST source identifier, which was calculated by the Hierarchical Triangular Mesh (HTM) algorithm [5] (the “HMpTy” package), and “ura” and “udec” are the equator coordinates to calculate “uid”. “gp_id” provides the corresponding source identifier in the Pan-STARRS, Gaia, or LAMOST, which depends on “ura” and “udec” of which survey were used to calculate “uid”.

The “obs_number”, “obsid_list”, “teff_lasp_list”, “logg_lasp_list”, and “feh_lasp_list” fields provide the observation number, unique spectrum ID list, effective temperature list, surface gravity list, and metallicity list, respectively. Because these targets were observed at multiple nights, their “obs_number” are all greater than 1. “exp_number”, “lmjm_list”, “rv_b0_list”, “rv_b1_list”, “rv_r0_list”, “rv_r1_list”, “rv_br0_list”, and “rv_br1_list” are the total exposure number, the “lmjm” list, and the radial velocity lists of red, blue and coadd spectra in each exposure, respectively, and these radial velocities are also provided in the LAMOST MRS General Catalog and the LAMOST MRS Parameter Catalog. In the fields with “_list”, the parameters obtained from each observation night are separated by the sign of “-”. It should be noted that, you can use each obsid in the “obsid_list” field to cross-match with other LAMOST MRS catalogs. 

By cross-matching with 11 SOS tables [6] of Gaia DR3, the variability types were obtained for variable sources in this table, and the “gaia_vari_type_sos” provides their variability types.

Here, we provide two formats of the LAMOST MRS Multiple Epoch Catalog to download, which include a FITS table and a CSV table, and they can be available from http://www.lamost.org/dr10/V2.0/catalogue.

Table 9: LAMOST MRS Multiple Epoch Catalog

Field (unit)

Type

Comment

uid

char

Unique source identifier calculated with the “ura” and “udec” in this table

ura (degree)

float

Right ascension used to calculate “uid”, and it may be from Gaia, Pan-STARRS, or LAMOST.

udec (degree)

float

Declination used to calculate “uid”, and it may be from Gaia, Pan-STARRS, or LAMOST.

gp_id

char

For each LAMOST source, the equatorial coordinates (“ura” and “udec” in this table) used to calculate “uid” were from which survey (Pan-STARRS, Gaia or LAMOST), “gp_id” gives the corresponding source identifier in that survey.

obs_number

int

Observation plan numbers for each target with multiple epoch observations

obsid_list

char

“obsid” list

teff_lasp_list

char

Effective temperature list

logg_lasp_list

char

Surface gravity list

feh_lasp_list

char

Metallicity list

exp_number

int

Total exposure number

lmjm_list

char

“lmjm” list

rv_b0_list

char

“rv_b0” list

rv_b1_list

char

“rv_b1” list

rv_r0_list

char

“rv_r0” list

rv_r1_list

char

“rv_r1” list

rv_br0_list

char

“rv_br0” list

rv_br1_list

char

“rv_br1” list

gaia_vari_type_sos

char

Variability types obtained by cross-matching with 11 Specific Object Studies (SOS) tables of Gaia DR3

 

3.4 LAMOST MRS Observed Plate Information Catalog

In this sub-section, we introduce the LAMOST MRS observed plate information catalog, which have the same table structure as the “Observed Plate Information Catalog” table in the low-resolution data release. Except the “obsdate” and “planid” fields also in other catalogs, other 7 basic information for 1,951 published plates were also included in this catalog as shown in table 10. The fields of “ra” and “dec” are the right ascension and declination of center star of each plate, and the field “mag” is the magnitude of center star. The field “seeing” is the dome seeing of the first exposure, and “exptime” is the total exposure time of n time exposures. The field “lmjm_list” is a string which provides the local modified Julian minute list for each plate, and it is separated by commas. For example, the “lmjm_list” for a plate is “84108765,84108789,84108813”, which represents the plate has three exposures, and it provides the local modified Julian minute at the beginning time of each exposure for this plate. Last, the “pid” is the unique ID of each plate.  
 
Here, we provide two formats of the LAMOST MRS observed plate information catalog to download, which include a FITS table and a CSV table, and they can be available from http://www.lamost.org/dr10/V2.0/catalogue.

Table 10: LAMOST MRS Observed Plate Information Catalog

Field (unit)

Type

Comment

pid

integer

Plate ID

obsdate

float

Target observation date

planid

char

Plan name

ra (degree)

float

Right ascension of center star

dec (degree)

float

Declination of center star

mag (mag)

float

Magnitude of center star

seeing

float

Seeing of the first exposure

exptime (second)

float

The total exposure time of n time exposures

lmjm_list

Integer

"lmjm" list        

 

3.5 LAMOST MRS Input Catalog

In this sub-section, we introduce the LAMOST MRS input catalog, which includes 27 parameters for 4,471,604 targets. There are 13 fields not included in previous tables, and they are the “unitid”, “epoch”, “tname”, “objtype”， “magtype”,“mag1”, “mag2”, “mag3”, “mag4”, “mag5”, “mag6” and “mag7” fields respectively. The “unitid” field is the ID of 4000 fiber units, “tname” is the unique ID of this catalog for each target, the value of “epoch” is “J2000”, “objtype” is the object class provided by the organizations or individuals who submitted the input catalogs, “magtype”gives the magnitude bands, and “mag1 ”-“mag7” is the magnitudes of the bands referred to “magtype”, which were given by the person or organization submitting the observation plan.

Here, we provide two formats of the LAMOST MRS input catalog to download, which include a FITS table and a CSV table, and they can be available from http://www.lamost.org/dr10/V2.0/catalogue.

Table 11: LAMOST MRS Input Catalog

Field (unit)

Type

Comment
obsid long integer Unique spectrum ID
obsdate float  Target observation date

planid

char

Plan name

spid

integer

Spectrograph ID

fiberid

integer

Fiber ID

unitid

char

ID of 4000 fiber units

ra_obs (degree)

float

Fiber pointing right ascension

dec_obs (degree)

float

Fiber pointing declination

objtype

char

Object type

magtype

char

Target magnitude type

mag1 (mag)

float

Associated magnitude 1

mag2 (mag)

float

Associated magnitude 2

mag3 (mag)

float

Associated magnitude 3

mag4 (mag)

float

Associated magnitude 4

mag5 (mag)

float

Associated magnitude 5

mag6 (mag)

float

Associated magnitude 6

mag7 (mag)

float

Associated magnitude 7

tsource

char

It is a preliminary classification label for each target used by the "fiber allocation procedure", and it generally denotes the organization and researcher who submits the target, the research subject to which the target belongs, and so on.

fibertype

char

Fiber type of target [Obj, Sky, F-std, Unused, PosErr, Dead]

tfrom

char

It is a further classification label for each target used by the "fiber allocation procedure", and it generally denotes the astronomical catalogues where the targets were chosen from, the target selection algorithm, and so on.

tcomment

char

This is a comment about each target and probably includes target ID in the astronomical catalogue where the target was chosen from, and/or the observed equatorial coordinate bias.

offsets

bool

Whether there is a fiber offset during observation

offsets_v (arcsec)

float

If the “offsets” field is true, “offsets_v” gives the offset distance from the target”s coordinator in input catalog          

ra (degree)

float

Right ascension from input catalog

dec (degree)

float

Declination from input catalog

epoch

char

J2000

tname

char

Unique ID for each targets in this catalog

 

Bibliography

1.    Liu, C., Bai, Z.R., Chen, J.J., et al. LAMOST Medium-Resolution Spectroscopic Survey (LAMOST-MRS): Scientific goals and survey plan, arxiv: 2005.07210.

2.    Huang, Y., Liu, X.W., Chen, B.Q., et al. 2018, A New Catalog of Radial Velocity Standard Stars from the APOGEE Data, AJ, 156, 90.

3.    Wang, R., Luo, A.L., Chen, J.J., et al. 2019, Properties of Radial Velocities measurement based on LAMOST-II Medium-Resolution Spectroscopic Observations, ApJS, 244, 27

4.    Zuo F., Luo, A.L., Du B., et al. 2024, Projected Rotational Velocities for LAMOST Stars with Effective Temperatures Lower than 9000K, ApJS, 271, 4

5.    Kunszt, Peter Z., Szalay, Alexander S., Thakar, Aniruddha R. The Hierarchical Triangular Mesh, Mining the Sky: Proceedings of the MPA/ESO/MPE Workshop Held at Garching, Germany, July 31 - August 4, 2000, ESO ASTROPHYSICS SYMPOSIA. ISBN 3-540-42468-7. Edited by A.J. Banday, S. Zaroubi, and M. Bartelmann. Springer-Verlag, 2001, p. 631

6.    Eyer, L., Audard, M., Holl, B., et al. Gaia Data Release 3. Summary of the variability processing and analysis. 2022, arXiv:2206.06416