- ID:
- ivo://CDS.VizieR/J/ApJ/885/74
- Title:
- 1340 Helium rich white dwarfs in the Gaia era
- Short Name:
- J/ApJ/885/74
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- We present an analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over the previous comprehensive studies on these types of objects. We use new trigonometric parallax measurements from the Gaia second data release, together with photometry from the Sloan Digital Sky Survey, Pan-STARRS, Gaia, or BVRI from the literature, which allow the determination of the mass for the majority of the objects in our sample. We use the photometric and spectroscopic techniques with our recently improved model atmospheres code, which include high-density effects, to accurately determine the effective temperature, surface gravity, and heavy-element abundances for each object. We study the abundance of hydrogen in DBZ/DZ white dwarfs and the properties of the accreted planetesimals. We explore the nature of the second sequence of DQ stars using proper motions from Gaia and highlight evidence of crystallization in massive DQ stars. We also present mass distributions for both spectral types. Finally, we discuss the implications of our findings in the context of the spectral evolution of white dwarfs and provide the atmospheric parameters for each star.
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Search Results
- ID:
- ivo://CDS.VizieR/III/135A
- Title:
- Henry Draper Catalogue and Extension
- Short Name:
- III/135A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An updated, corrected, and extended machine-readable version of The Henry Draper Catalogue (HD, Cannon & Pickering 1918-1924) is available with documentation from the Astronomical Data Center (ADC) as of April 1989. Published and unpublished errors discovered in the previous version have been corrected; letters indicating supplemental stars in the BD have been moved to a new byte to distinguish them from double-star components; and the machine-readable portion of The Henry Draper Extension (HDE) (HA 100; Cannon 1925-1936) has been converted to the same format as the main catalog with additional data added as necessary. The catalog lists HD numbers, Durchmusterung numbers, positions for equinox B1900, photovisual and photographic magnitudes, spectral types, codes for the intensity of the spectra used, and remarks.
- ID:
- ivo://CDS.VizieR/J/A+AS/136/429
- Title:
- Herbig Ae/Be stars candidates
- Short Name:
- J/A+AS/136/429
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed 42 Herbig Ae/Be stars candidates in both hemispheres using the high resolution spectrographs AURELIE and ELODIE at OHP, and CES at ESO. Table 1 present the journal of our spectroscopic observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/863/13
- Title:
- Herschel obs. of protoplanetary disks in L1641
- Short Name:
- J/ApJ/863/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze Herschel Space Observatory observations of 104 young stellar objects with protoplanetary disks in the ~1.5Myr star-forming region Lynds 1641 (L1641) within the Orion A Molecular Cloud. We present spectral energy distributions from the optical to the far-infrared including new photometry from the Herschel Photodetector Array Camera and Spectrometer at 70{mu}m. Our sample, taken as part of the Herschel Orion Protostar Survey, contains 24 transitional disks, 8 of which we identify for the first time in this work. We analyze the full disks (FDs) with irradiated accretion disk models to infer dust settling properties. Using forward modeling to reproduce the observed n_Ks-[70]_ index for the FD sample, we find the observed disk indices are consistent with models that have depletion of dust in the upper layers of the disk relative to the midplane, indicating significant dust settling. We perform the same analysis on FDs in Taurus with Herschel data and find that Taurus is slightly more evolved, although both samples show signs of dust settling. These results add to the growing literature that significant dust evolution can occur in disks by ~1.5Myr.
- ID:
- ivo://CDS.VizieR/J/AJ/159/30
- Title:
- High proper-motion M-type stars spectroscopic obs.
- Short Name:
- J/AJ/159/30
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- Large numbers of low-to-medium-resolution spectra of M-type dwarf stars from both the local Galactic disk and halo are available from various surveys. In order to fully exploit these data, we develop a template-fit method using a set of empirically assembled M dwarf/subdwarf classification templates, based on the measurements of the TiO and CaH molecular bands near 7000{AA}, which are used to classify M dwarfs/subdwarfs by spectral type and metallicity class. We further present a pipeline to automatically determine the effective temperature Teff, metallicity [M/H], {alpha}-element to iron abundance ratio [{alpha}/Fe], and surface gravity logg of M dwarfs/subdwarfs using the latest version of BT-Settl model atmospheres. We apply these methods to a set of low-to-medium-resolution spectra of 1544 high proper-motion ({mu}>=0.4"/yr) M dwarfs/subdwarfs, collected at the MDM observatory, Lick Observatory, Kitt-Peak National Observatory, and Cerro-Tololo Interamerican Observatory.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/70
- Title:
- Hot subdwarf stars from Gaia DR2 and LAMOST DR5
- Short Name:
- J/ApJ/868/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 4593 hot subdwarf candidates from the Gaia DR2 Hertzsprung-Russell (HR) diagram. By combining the sample with Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we identified 294 hot subdwarf stars, including 169 sdB, 63 sdOB, 31 He-sdOB, 22 sdO, 7 He-sdO, and 2 He-sdB stars. The atmospheric parameters (e.g., Teff, logg, log(nHe/nH)) are obtained by fitting the hydrogen (H) and helium (He) line profiles with synthetic spectra. Two distinct He sequences of hot subdwarf stars are clearly presented in the Teff-logg diagram. We found that the He-rich sequence consists of the bulk of sdB and sdOB stars, as well as all of the He-sdB, He-sdO, and He-sdOB stars in our samples, while all the stars in the He-weak sequence belong to the sdO spectral type, combined with a few sdB and sdOB stars. We demonstrated that the combination of Gaia DR2 and LAMOST DR5 allows one to uncover a huge number of new hot subdwarf stars in our Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/135
- Title:
- Hot subdwarf stars from Gaia DR2 and LAMOST DR5. II.
- Short Name:
- J/ApJ/881/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Three hundred and eighty eight hot subdwarf stars have been identified by using the Hertzsprung-Russell (HR) diagram built from the second data release of the Gaia mission. By analyzing their observed Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectra, we characterized 186 sdB, 73 He-sdOB, 65 sdOB, 45 sdO, 12 He-sdO, and 7 He-sdB stars. The atmospheric parameters of these stars (e.g., Teff, logg, log(nHe/nH)) are obtained by fitting the hydrogen (H) and helium (He) line profiles with synthetic spectra calculated from non-local thermodynamic equilibrium model atmospheres. Among these stars, we have 135 new identified hot subdwarfs which have not been cataloged before. Although 253 stars appear in the catalog by Geier+ (2017, J/A+A/600/A50), only 91 of them have atmospheric parameters. Together with the 294 hot subdwarf stars found by Lei+ (Paper I, 2018, J/ApJ/868/70), we identified 682 hot subdwarf stars in total by using the Gaia HR-diagram and LAMOST spectra. These results demonstrate the efficiency of our method to combine large surveys to search for hot subdwarf stars. We found a distinct gap in our He-sdOB stars based on their He abundance, which is also presented in extreme horizontal branch (EHB) stars of the globular cluster {omega} Cen. The number fraction of the sample size for the two subgroups is very different between the two counterparts. However, the distinct gap between the H-sdB stars and He-sdOB stars in {omega} Cen is not visible in our sample. More interestingly, the He-sdB population with the highest He abundance in our sample is completely missing in {omega} Cen. The discrepancy between our field hot subdwarf stars and the EHB stars in {omega} Cen indicate different origins for the two counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/117
- Title:
- Hot subdwarf stars from Gaia DR2 & LAMOST DR6+7. I.
- Short Name:
- J/ApJ/889/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 182 single-lined hot subdwarf stars are identified by using spectra from the sixth and seventh data releases (DR6 and DR7) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope survey. We classified all the hot subdwarf stars using a canonical classification scheme, and got 89 sdB, 37 sdOB, 26 sdO, 24 He-sdOB, 3 He-sdO, and 3 He-sdB stars, respectively. Among these stars, 108 hot subdwarfs are newly discovered, while 74 stars were reported by previous catalogs. The atmospheric parameters of these stars were obtained by fitting the hydrogen (H) and helium (He) lines with non-local thermodynamic equilibrium model atmospheres. The atmospheric parameters confirm the two He sequences and the two subgroups of He-sdOB stars in our samples, which were found by previous studies in the T_eff_-log(nHe/nH) diagram. Our results demonstrate different origins of field hot subdwarf stars and extreme horizontal branch stars in globular clusters, and provide strict observational limits on the formation and evolution models of the different sub-types of these evolved objects. Based on the results, we evaluated the completeness of the Geier+ (2017, J/A+A/600/A50) catalog. We found the fraction of hot subwarf stars is between 10% and 60%, depending on the brightness of the sample. A more accurate estimation for the hot subdwarf fraction can be obtained when similar results from composite spectra will become available.
- ID:
- ivo://CDS.VizieR/J/AJ/159/119
- Title:
- HST emission line survey of Andromeda. I. Be stars
- Short Name:
- J/AJ/159/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a two epoch Hubble Space Telescope H{alpha} emission line survey of the Andromeda galaxy that overlaps the footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We found 552 (542) classical Be stars and 8429 (8556) normal B-type stars in epoch 1 (epoch 2), yielding an overall fractional Be content of 6.15%{+/-}0.26% (5.96%{+/-}0.25%). The fractional Be content decreased with spectral subtype from ~23.6%{+/-}2.0% (~23.9%{+/-}2.0%) for B0-type stars to ~3.1%{+/-}0.34% (~3.4%{+/-}0.35%) for B8-type stars in epoch 1 (epoch 2). We observed a clear population of cluster Be stars at early fractional main-sequence lifetimes, indicating that a subset of Be stars emerge onto the zero-age main sequence as rapid rotators. Be stars are 2.8x rarer in M31 for the earliest subtypes compared to the Small Magellanic Cloud, confirming that the fractional Be content decreases in significantly more metal-rich environments (like the Milky Way and M31). However, M31 does not follow a clear trend of Be fraction decreasing with metallicity compared to the Milky Way, which may reflect that the Be phenomenon is enhanced with evolutionary age. The rate of disk-loss or disk-regeneration episodes we observed, 22%{+/-}2%/yr, is similar to that observed for seven other Galactic clusters reported in the literature, assuming these latter transient fractions scale by a linear rate. The similar number of disk-loss events (57) as disk-renewal events (43) was unexpected since disk dissipation timescales can be ~2x the typical timescales for disk build-up phases.
- ID:
- ivo://CDS.VizieR/J/AJ/151/23
- Title:
- HST photometry of stars in HD 97950
- Short Name:
- J/AJ/151/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use photometry in the F220W, F250W, F330W, F435W filters from the High Resolution Channel of the Advanced Camera for Surveys and photometry in the F555W, F675W, and F814W filters from the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope to derive individual stellar reddenings and extinctions for stars in the HD97950 cluster in the giant HII region NGC 3603. The mean line of sight reddening for about a hundred main-sequence member stars inside the cluster is E(F435W-F555W)=1.33+/-0.12mag. After correcting for foreground reddening, the total to selective extinction ratio is R_F555W_=3.75+/-0.87 in the cluster. Within the standard deviation associated with E({lambda}-F555W)/E(F435W-F555W) in each filter, the cluster extinction curve at ultraviolet wavelengths tends to be grayer than the average Galactic extinction laws from Cardelli et al. and Fitzpatrick. It is closer to the extinction law derived by Calzetti et al. for starburst galaxies, where the 0.2175{mu}m bump is absent. This indicates an anomalous extinction in the HD97950 cluster, which may due to the clumpy dust distribution within the cluster, and the size of dust grains being larger than the average Galactic ISM.
