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Register a new userThree Moving Groups Detected in the LAMOST DR1 Archive
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We analyze the kinematics of thick disk and halo stars observed by the Large sky Area Multi-Object Fiber Spectroscopic Telescope. We have constructed a sample of 7,993 F, G and K nearby main-sequence stars (textit{d} $<$ 2 kpc) with estimates of position (x, y, z) and space velocity ($U$, $V$, $W$) based on color and proper motion from the SDSS DR9 catalog. Three `phase-space overdensities are identified in [textit{V}, $sqrt{U^{2}+2V^{2}}$] with significance levels of $sigma$ $>$ 3. %[L$_{Z}$, eccentricity], [L$_{Z}$, L$_{bot}$], and [V$_{az}$, V$_{triangle}E$]. Two of them (Hyades-Pleiades stream, Arcturus-AF06 stream) have been identified previously. We also find evidence for a new stream (centered at textit{V} $sim$ -180 km s$^{-1}$) in the halo. The formation mechanisms of these three streams are analyzed. Our results support the hypothesis the Arcturus-AF06 stream and the new stream originated from the debris of a disrupted satellite, while Hyades-Pleiades stream has a dynamical origin.
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In this work, we present a systematic search for stellar groups in the Taurus field by applying DBSCAN algorithm to the data from Gaia DR2. We find 22 groups, consisting of 8 young groups (Groups 1-8) at ages of 2-4Myr and distances of ~130-170pc, 14 old groups (Groups 9-22) at ages of 8-49Myr and distances of ~110-210pc. We characterize the disk properties of group members and find 19 new disk-bearing stars, 8 of which are in the young groups and 11 others belong to the comparatively old groups at ages of 8-11 Myr. We characterize the accretion properties of the group members with H$alpha$ emission line in their LAMOST spectra, and discover one source in Group 10 at an age of 10 Myr which still shows accretion activity. We investigate the kinematic relations among the old groups, and find that Group 9 is kinematically related to the known Taurus members and exclude any kinematic relations between Groups 10-22 and the known Taurus members.
We report on searching for Classical B-type emission-line (CBe) stars from the first data release (DR1) of the Large Sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST; also named the Guoshoujing Telescope). A total of 192 (12 known CBes) objects were identified as CBe candidates with prominent He~I~$lambda4387$, He~I~$lambda4471$, and Mg~II~$lambda4481$ absorption lines, as well as H$beta$~$lambda4861$ and H$alpha$~$lambda6563$ emission lines. These candidates significantly increases current CBe sample of about 8%. Most of the CBe candidates are distributed at the Galactic Anti-Center due to the LAMOST observing strategy. Only two of CBes are in the star clusters with ages of 15.8 and 398~Myr, respectively.
Context. White dwarf-main sequence (WDMS) binaries are used to study several different important open problems in modern astrophysics. Aims. The Sloan Digital Sky Survey (SDSS) identified the largest catalogue of WDMS binaries currently known. However, this sample is seriously affected by selection effects and the population of systems containing cool white dwarfs and early-type companions is under-represented.Here we search for WDMS binaries within the spectroscopic data release 1 of the LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) survey. LAMOST and SDSS follow different target selection algorithms. Hence, LAMOST WDMS binaries may be drawn from a different parent population and thus help in overcoming the selection effects incorporated by SDSS on the current observed population. Methods. We develop a fast and efficient routine based on the wavelet transform to identify LAMOST WDMS binaries containing a DA white dwarf and a M dwarf companion, and apply a decomposition/fitting routine to their LAMOST spectra to estimate their distances and measure their stellar parameters, namely the white dwarf effective temperatures, surface gravities and masses, and the secondary star spectral types. Results. We identify 121 LAMOST WDMS binaries, 80 of which are new discoveries, and estimate the sample to be sim90 per cent complete. The LAMOST and SDSS WDMS binaries are found to be statistically different. However, this result is not due to the different target selection criteria of both surveys, but likely a simple consequence of the different observing conditions. Thus, the LAMOST population is found at considerably shorter distances (sim50-450 pc) and is dominated by systems containing early-type companions and hot white dwarfs. (abridged)
We present the results of a study of the stellar activity in the solar neighborhood using complete kinematics (galactocentric velocities U,V,W) and the chromospheric activity index $log R_{rm{HK}}$. We analyzed the average activity level near the centers of known moving groups using a sample of 2529 stars and found that the stars near these associations tend to be more active than field stars. This supports the hypothesis that these structures, or at least a significant part of them, are composed of kinematically bound, young stars. We confirmed our results by using Galaxy Evolution Explorer (GALEX) UV data and kinematics taken from the Geneva-Copenhagen Survey for the stars in the sample. Finally, we present a compiled catalog with kinematics and activities for 2529 stars and a list of potential moving group members selected based on their stellar activity level.
The presence of three more Herbig Ae/Be (HAeBe) stars in the Cepheus Flare within a 1.5$^{circ}$ radius centered on HD 200775 suggests that star formation is prevalent in a wider region of the LDN 1147/1158, LDN 1172/1174, and LDN 1177 clouds. A number of young stellar objects (YSOs) are also found to be located toward these clouds. Various star formation studies indicate ongoing low-mass star formation inside this region. Sources associated with less near-infrared (IR) excess and less H-alpha emission raise the possibility that more low-mass YSOs, which were not identified in previous studies, are present in this region. The aim is to conduct a search for additional young sources that are kinematically associated with the known YSOs and to characterize their properties. Based on the Gaia DR2 distances and proper motions, we found that BD+68 1118, HD 200775, and PV Cep are spatially and kinematically associated with known YSOs. Using the Gaia DR2 data, we identified 39 co-moving sources around BD+68 1118. These sources are characterized using optical and near-IR color-color and color-magnitude diagrams. We estimated a distance of 340+/-7 pc to the whole association that contains BD+68 1118, HD 200775, and PV Cep. Based on the distance and proper motions of all the known YSOs, a total of 74 additional co-moving sources are found, of which 39 form a loose association surrounding BD+68 1118. These sources are predominantly M-type with ages of $sim$10 Myr and no or very little near-IR excess emission. The positive expansion coefficients obtained via the projected internal motions of the sources surrounding BD+68 1118 and HD 200775 show that these sources are expanding with respect to their HAeBe stars. A spatio-temporal gradient of these sources toward the center of the Cepheus Flare Shell supports the concept of star formation triggered by external impacts.
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