The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

Jeffery, C. S.; Miszalski, B.; Snowdon, E J

doi:10.1093/mnras/staa3648

Cited by 29 publications

(39 citation statements)

References 74 publications

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“…The He abundance of Group eHe-1 is nearly independent of temperature. A similar result was reported by Jeffery et al (2021). The number of stars in Group iHe-1 and iHe-2 display a significant difference: the former group has 65 members, but the later includes only 17 stars.…”

Section: Calculations Of Galactic Space Velocities and Orbital Parame...supporting

confidence: 86%

Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7

Luo,

Nemeth,

Wang

et al. 2021

Preprint

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Based on the Gaia DR2 catalogue of hot subdwarf star candidates, we identified 1587 hot subdwarf stars with spectra in LAMOST DR7. We present atmospheric parameters for these stars by fitting the LAMOST spectra with Tlusty/Synspec non-LTE synthetic spectra. Combining LAMOST radial velocities and Gaia Early Data Release 3 (EDR3) parallaxes and proper motions, we also present the Galactic space positions, velocity vectors, orbital parameters and the Galactic population memberships of the stars. With our He classification scheme, we identify four groups of He rich hot subdwarf stars in the T eff − log g and T eff − log (nHe/nH) diagrams. We find two extreme He-rich groups (eHe-1 and eHe-2) for stars with log (nHe/nH) ≥ 0 and two intermediate He-rich groups (iHe-1 and iHe-2) for stars with −1 ≤ log (nHe/nH) < 0. We also find that over half of the stars in Group eHe-1 are thick disk stars, while over half of the stars in Group eHe-2 correspond to thin disk stars. The disk population fractions of Group iHe-1 are between those of Group eHe-1 and eHe-2. Almost all stars in Group iHe-2 belong to the thin disk. These differences indicate that the four groups probably have very different origins. Comparisons between hot subdwarf stars in the halo and in the Galactic globular cluster ω Cen show that only He-deficient stars with −2.2 ≤ log (nHe/nH) < −1 have similar fractions. Hot subdwarfs with log (nHe/nH) ≥ 0 in ω Cen have no counterparts in the thick disk and halo populations, but they appear in the thin disk.

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Section: Calculations Of Galactic Space Velocities and Orbital Parame...supporting

confidence: 86%

Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7

Luo,

Nemeth,

Wang

et al. 2021

Preprint

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“…For hot subdwarfs, LTE remains a good approximation for the structure of the model atmosphere, up to effective temperatures ≈ 30 000 K (Anderson & Grigsby 1991) the inclusion of all relevant opacity being more critical. Jeffery et al (2021) found fully-blanketed LTE models more satisfactory than zerometal non-LTE models up to effective temperatures ≈ 40 000 K. The approximation is also convenient since can easily be adapted by us to include new physics, such as additional opacities.…”

Section: O R I Gmentioning

confidence: 98%

Electron-Impact Excitation of Ge iii and Photoionisation of Ge ii

Dunleavy

Ballance

Ramsbottom

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Energy levels, Einstein A-values and oscillator strengths are calculated for doubly-ionised germanium (Ge iii). We have undertaken a study of the electron-impact excitation of Ge iii and have also completed a study of the photoionisation of Ge ii. Ge iii target structures were generated using the relativistic GRASP0 package. Several scattering models were investigated to assess the uncertainty quantification of our results. Initially, the lowest lying 64 jj fine-structure levels were included in the close-coupling expansion resulting from 14 non-relativistic configurations. A second larger model was subsequently generated using the GASP package and incorporated the lowest 589 jj fine-structure levels from 17 non-relativistic configurations. Both the DARC and Breit-Pauli parallel suite of R-matrix collision codes were utilised in the scattering calculations to generate the collision strengths for incident electron-energies between 0 and 5 Rydbergs and subsequently the Maxwellian averaged effective collision strengths for temperatures in the range 1000 to 200000 Kelvin. The photoionisation calculations comprised of two studies, a DARC and a Breit-Pauli calculation incorporating the 250 lowest lying levels. Photoionisation cross sections for Ge ii are presented in the range 0-5 Ryds. Due to the lack of data available in the literature, the present radiative data and electron-impact/photoionisation cross sections are compared between the models presented in this paper. To assess their significance for astrophysics, the data are incorporated into the stellar atmosphere package sterne. Test models for the heavy-metal subdwarf LSIV−14○116 are not affected by the new data, but models for cooler stars may be sensitive to them.

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“…Four of the targets show both flux and color excess. One of them, GaiaJ2223-2510, is a heavily polluted DB white dwarf (Jeffery et al 2020) previously mis-identified as a hot subdwarf (Geier et al 2017). Another target, GaiaJ0147+2329, is a known infrared variable with a dusty debris disk also known as Gaia 0145+234 (Wang et al 2019).…”

Section: Spitzer-confirmed Infrared Excesses (Samples A-e)mentioning

confidence: 99%

Infrared Excesses Around Bright White Dwarfs from Gaia and unWISE. II

Lai

Dennihy

et al. 2021

ApJ

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Infrared excesses around white dwarf stars indicate the presence of various astrophysical objects of interest, including companions and debris disks. In this second paper of a series, we present follow-up observations of infrared excess candidates from Gaia and unWISE discussed in the first paper, Paper I. We report space-based infrared photometry at 3.6 and 4.5 micron for 174 white dwarfs from the Spitzer Space Telescope and groundbased near-infrared J, H, and K photometry of 235 white dwarfs from Gemini Observatory with significant overlap between Spitzer and Gemini observations. These data are used to confirm or rule out the observed unWISE infrared excess. From the unWISE-selected candidate sample, the most promising infrared excess sample comes from both color and flux excess, which has a Spitzer confirmation rate of 95%. We also discuss a method to distinguish infrared excess caused by stellar or sub-stellar companions from potential dust disks. In total, we confirm the infrared excess around 62 white dwarfs, 10 of which are likely to be stellar companions. The remaining 52 bright white dwarfs with infrared excess beyond two microns has the potential to double the known sample of white dwarfs with dusty exoplanetary debris disks. Follow-up high-resolution spectroscopic studies of a fraction of confirmed excess white dwarfs in this sample have discovered emission from gaseous dust disks. Additional investigations will be able to expand the parameter space from which dust disks around white dwarfs are found. Unified AstronomyThesaurus concepts: White dwarf stars (1799); Stellar accretion disks (1579); Brown dwarfs (185); M dwarf stars (982); Debris disks (363); Near infrared astronomy (1093); Infrared astronomy (786); Infrared excess (788)

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The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

Cited by 29 publications

References 74 publications

Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7

Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7

Electron-Impact Excitation of Ge iii and Photoionisation of Ge ii

Infrared Excesses Around Bright White Dwarfs from Gaia and unWISE. II

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