The Large sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) general survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10 million spectra of stars, galaxies and QSOs. Objects in both the pilot survey and the first year regular survey are included in the LAMOST DR1. The pilot survey started in October 2011 and ended in June 2012, and the data have been released to the public as the LAMOST Pilot Data Release in August 2012. The regular survey started in September 2012, and completed its first year of operation in June 2013. The LAMOST DR1 includes a total of 1202 plates containing 2955336 spectra, of which 1790879 spectra have observed signal-to-noise ratio (SNR)>=10. All data with SNR>=2 are formally released as LAMOST DR1 under the LAMOST data policy. This data release contains a total of 2204696 spectra, of which 1944329 are stellar spectra, 12082 are galaxy spectra and 5017 are quasars. The DR1 not only includes spectra, but also three stellar catalogs with measured parameters: late A,FGK-type stars with high quality spectra (1061918 entries), A-type stars (100073 entries), and M-type stars (121522 entries). This paper introduces the survey design, the observational and instrumental limitations, data reduction and analysis, and some caveats. A description of the FITS structure of spectral files and parameter catalogs is also provided.
Phase II of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)-Kepler/K2 survey (LK-MRS), initiated in 2018, aims at collecting medium-resolution spectra (R~7500; hereafter MRS) for more than 50000 stars with multiple visits (~60 epochs) over a period of 5yr (2018 September to 2023 June). We selected 20 footprints distributed across the Kepler field and six K2 campaigns, with each plate containing a number of stars ranging from ~2000 to ~3000. During the first year of observations, the LK-MRS has already visited 13 plates 223 times over 40 individual nights, and collected ~280000 and ~369000 high-quality spectra in the blue and red wavelength ranges, respectively. The atmospheric parameters and radial velocities for ~259000 spectra of 21053 targets were successfully calculated by the LAMOST stellar parameter pipeline. The internal uncertainties for the effective temperature, surface gravity, metallicity, and radial velocity are found to be 100K, 0.15dex, 0.09dex, and 1.00km/s, respectively, when derived from a medium-resolution LAMOST spectrum with a signal-to-noise ratio (S/N) in the g band of 10. All of the uncertainties decrease as S/N increases, but they stabilize for S/N>100. We found 14997, 20091, and 1514 stars in common with the targets from the LAMOST low-resolution survey (LRS), Gaia, and the Apache Point Observatory Galactic Evolution Experiment (APOGEE), respectively, corresponding to fractions of ~70%, ~95%, and ~7.2%. In general, the parameters derived from LK-MRS spectra are consistent with those obtained from the LRS and APOGEE spectra, but the scatter increases as the surface gravity decreases when comparing with the measurements from APOGEE. A large discrepancy is found with the Gaia values of the effective temperature. Comparisons of the radial velocities of LK-MRS to Gaia and LK-MRS to APOGEE nearly follow a Gaussian distribution with means of {mu}~1.10 and 0.73km/s, respectively. We expect that the results from the LK-MRS spectra will shed new light on binary stars, asteroseismology, stellar activity, and other research fields.
We present a sample of 48 metal-poor galaxies at z<0.14 selected from 92 510 galaxies in the LAMOST survey. These galaxies are identified by their detection of the auroral emission line [OIII]{lambda}4363 above the 3{sigma} level, which allows a direct measurement of electron temperature and oxygen abundance. The emission line fluxes are corrected for internal dust extinction using the Balmer decrement method. With electron temperature derived from [OIII]{lambda}{lambda}4959,5007/[OIII]{lambda}4363 and electron density from [SII]{lambda}6731/[SII]{lambda}6717, we obtain the oxygen abundances in our sample which range from 12+log(O/H)=7.63(0.09Z_{sun}_) to 8.46 (0.6Z_{sun}_). We find an extremely metal-poor galaxy with 12+log(O/H)=7.63+/-0.01. With multiband photometric data from FUV to NIR and H{alpha} measurements, we also determine the stellar masses and star formation rates, based on the spectral energy distribution fitting and H{alpha} luminosity, respectively. We find that our galaxies have low and intermediate stellar masses with 6.39<=log(M/M_{sun}_)<=9.27, and high star formation rates (SFRs) with -2.18<=log(SFR/M_{sun}_yr^-1^)<=1.95. We also find that the metallicities of our galaxies are consistent with the local T_e_-based mass-metallicity relation, while the scatter is about 0.28dex. Additionally, assuming the coefficient of {alpha}=0.66, we find most of our galaxies follow the local mass-metallicity-SFR relation, but a scatter of about 0.24dex exists, suggesting the mass-metallicity relation is weakly dependent on SFR for those metal-poor galaxies.
The nearly continuous light curves with micromagnitude precision provided by the space mission Kepler are revolutionizing our view of pulsating stars. They have revealed a vast sea of low-amplitude pulsation modes that were undetectable from Earth. The long time base of Kepler light curves allows for the accurate determination of the frequencies and amplitudes of pulsation modes needed for in-depth asteroseismic modeling. However, for an asteroseismic study to be successful, the first estimates of stellar parameters need to be known and they cannot be derived from the Kepler photometry itself. The Kepler Input Catalog provides values for the effective temperature, surface gravity, and metallicity, but not always with sufficient accuracy. Moreover, information on the chemical composition and rotation rate is lacking. We are collecting low-resolution spectra for objects in the Kepler field of view with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, Xinglong observatory, China). All of the requested fields have now been observed at least once. In this paper, we describe those observations and provide a useful database for the whole astronomical community.
LAMOST Quasar Survey: quasar properties from DR2&3
Short Name:
J/AJ/155/189
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the second installment for the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed from 2013 September to 2015 June. There are 9024 confirmed quasars in DR2 and 10911 in DR3. After cross-match with the Sloan Digital Sky Survey (SDSS) quasar catalogs and NED, 12126 quasars are discovered independently. Among them, 2225 quasars were released by SDSS DR12 QSO catalog in 2014 after we finalized the survey candidates. 1801 sources were identified by SDSS DR14 as QSOs. The remaining 8100 quasars are considered as newly founded, and among them, 6887 quasars can be given reliable emission line measurements and the estimated black hole masses. Quasars found in LAMOST are mostly located at low-to-moderate redshifts, with a mean value of 1.5. The highest redshift observed in DR2 and DR3 is 5. We applied emission line measurements to H{alpha}, H{beta}, Mg II, and C IV. We deduced the monochromatic continuum luminosities using photometry data, and estimated the virial black hole masses for the newly discovered quasars. Results are compiled into a quasar catalog, which will be available online.
LAMOST quasar survey: quasar properties from the DR1
Short Name:
J/AJ/151/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present preliminary results of the quasar survey in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) first data release (DR1), which includes the pilot survey and the first year of the regular survey. There are 3921 quasars reliably identified, among which 1180 are new quasars discovered in the survey. These quasars are at low to median redshifts, with a highest z of 4.83. We compile emission line measurements around the H{alpha}, H{beta}, Mg II, and C IV regions for the new quasars. The continuum luminosities are inferred from SDSS photometric data with model fitting, as the spectra in DR1 are non-flux-calibrated. We also compile the virial black hole mass estimates, with flags indicating the selection methods, and broad absorption line quasars. The catalog and spectra for these quasars are also available. Of the 3921 quasars, 28% are independently selected with optical-infrared colors, indicating that the method is quite promising for the completeness of the quasar survey. LAMOST DR1 and the ongoing quasar survey will provide valuable data for studies of quasars.
We present a new analysis of the LAMOST DR1 survey spectral database performed with the code SP_Ace, which provides the derived stellar parameters Teff, logg, [Fe/H], and [alpha/H] for 1,097,231 stellar objects. We tested the reliability of our results by comparing them to reference results from high spectral resolution surveys. The expected errors can be summarized as ~120K in Teff, ~0.2 in logg, ~0.15dex in [Fe/H], and ~0.1dex in [alpha/Fe] for spectra with S/N>40, with some differences between dwarf and giant stars. SP_Ace provides error estimations consistent with the discrepancies observed between derived and reference parameters. Some systematic errors are identified and discussed. The resulting catalog is publicly available at the LAMOST and CDS websites.
We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z<0.05) Seyfert 1 galaxies with expected masses in the range ~10^6^-10^7^M_{sun}_ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad H{beta} emission, which we have previously reported. We present here the light curves for the H{alpha}, H{gamma}, HeII{lambda}4686, and HeI{lambda}5876 emission lines and the time lags for the emission-line responses relative to changes in the continuum flux.
We present measurements of the optical/UV emission lines for a large homogeneous sample of 993 quasars from the Large Bright Quasar Survey. Our largely automated technique accounts for continuum breaks and galactic reddening, and we perform multicomponent fits to emission line profiles, including the effects of blended iron emission, and of absorption lines both galactic and intrinsic. Here we describe the fitting algorithm and present the results of line fits to the LBQS sample, including upper limits to line equivalent widths when warranted. The distribution of measured line parameters, principally W_{lambda}_ and FWHM, are detailed for a variety of lines, including upper limits. We thus initiate a large-scale investigation of correlations between the high-energy continuum and emission lines in quasars, to be extended to complementary samples using similar techniques. High-quality, reproducible measurements of emission lines for uniformly selected samples will advance our understanding of active galaxies, especially in a new era of large surveys selected by a variety of complementary methods.
Understanding the dominant heating mechanism in the nuclei of galaxies is crucial to understand star formation in starbursts (SB), active galactic nuclei (AGN) phenomena and the relationship between the star formation and AGN activity in galaxies. The analysis of the carbon monoxide (^12^CO) rotational ladder versus the infrared continuum emission (hereafter, ^12^CO/IR) in galaxies with different type of activity have shown important differences between them. We aim at carrying out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy by a multi-transitions analysis of the spatial distribution of the ^12^CO emission at different spatial scales. We also want to establish the dominant heating mechanism at work in the inner region of this object at smaller spatial scales (<~200pc). We present far-infrared (FIR) and sub-millimeter (sub-mm) ^12^CO line maps and single spectra (from J_up_=3 to 20) using the Heterodyne Instrument for the Far Infrared (HIFI), the Photoconductor Array Camera and Spectrometer (PACS), and the Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, and the Atacama Pathfinder EXperiment (APEX). We combined the ^12^CO/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the ^12^CO images to derive the thermal structure of the Interstellar Medium (ISM) for spatial scales raging from <~200pc to 2kpc. In addition, we also present single spectra of low (^12^CO, ^13^CO and [CI]) and high density (HCN, HNC, HCO^+^, CS and CH) molecular gas tracers obtained with APEX and HIFI applying LTE and non-LTE analyses. Furthermore, the Spectral Energy Distribution (SED) of the continuum emission from the far-IR to sub-mm wavelengths is also presented. From the non-LTE analysis of the low and high density tracers we derive in NGC 4945 gas volume densities (10^3^-10^6^cm^-3^) similar to those found in other galaxies with different type of activity. From the ^12^CO analysis we found clear trend in the distribution of the derived temperatures and the ^12^CO/IR ratios. It is remarkable that at intermediate scales (360pc-1kpc, or 19"-57") we see large temperatures in the direction of the X-ray outflow while at smaller scales (<~200pc-360pc, or 9"-19"), the highest temperature, derived from the high-J lines, is not found toward the nucleus, but toward the galaxy plane. The thermal structure derived from the ^12^CO multi-transition analysis suggests that mechanical heating, like shocks or turbulence, dominates the heating of the ISM in the nucleus of NGC4945 located beyond 100 pc (&500) from the center of the galaxy. This result is further supported by the Kazandjian et al. (2015, Cat. J/AJ/133/504) models, which are able to reproduce the emission observed at high-J (PACS) ^12^CO transitions when mechanical heating mechanisms are included. Shocks and/or turbulence are likely produced by the barred potential and the outflow, observed in X-rays.
