Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/467/4970
- Title:
- Cool DZ white dwarfs. I.
- Short Name:
- J/MNRAS/467/4970
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- White dwarfs with metal lines in their spectra act as signposts for post-main-sequence planetary systems. Searching the Sloan Digital Sky Survey (SDSS) Data Release 12, we have identified 231 cool (<9000K) DZ white dwarfs with strong metal absorption, extending the DZ cooling sequence to both higher metal abundances and lower temperatures, and hence longer cooling ages. Of these 231 systems, 104 are previously unknown white dwarfs. Compared with previous work, our spectral fitting uses improved model atmospheres with updated line profiles and line-lists, which we use to derive effective temperatures and abundances for up to eight elements. We also determine spectroscopic distances to our sample, identifying two halo members with tangential space velocities >300km/s. The implications of our results on remnant planetary systems are to be discussed in a separate paper.
- ID:
- ivo://CDS.VizieR/J/AJ/142/103
- Title:
- Cool evolved stars in SAGE-SMC and SAGE-LMC
- Short Name:
- J/AJ/142/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC", or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160um). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ~20% of the global SMC flux (extended + point-source) at 3.6um, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1592
- Title:
- Cool stars in galactic clusters
- Short Name:
- J/MNRAS/403/1592
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated the relevant trend of the bolometric correction (BC) at the cool-temperature regime of red giant stars and its possible dependence on stellar metallicity. Our analysis relies on a wide sample of optical-infrared spectroscopic observations, along the 3500{AA}=>2.5um wavelength range, for a grid of 92 red giant stars in five (three globular + two open) Galactic clusters, along the full metallicity range covered by the bulk of the stars, -2.2<=[Fe/H]<=+0.4.
- ID:
- ivo://CDS.VizieR/J/ApJ/878/63
- Title:
- Cool WD atmosphere models. IV. Spectral evolution
- Short Name:
- J/ApJ/878/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As a result of competing physical mechanisms, the atmospheric composition of white dwarfs changes throughout their evolution, a process known as spectral evolution. Because of the ambiguity of their atmospheric compositions and the difficulties inherent to the modeling of their dense atmospheres, no consensus exists regarding the spectral evolution of cool white dwarfs (Teff<6000K). In the previous papers of this series, we presented and observationally validated a new generation of cool white dwarf atmosphere models that include all the necessary constitutive physics to accurately model those objects. Using these new models and a homogeneous sample of 501 cool white dwarfs, we revisit the spectral evolution of cool white dwarfs. Our sample includes all spectroscopically identified white dwarfs cooler than 8300K for which a parallax is available in Gaia DR2 and photometric observations are available in Pan-STARRS1 and 2MASS. Except for a few cool carbon-polluted objects, our models allow an excellent fit to the spectroscopic and photometric observations of all objects included in our sample. We identify a decrease of the ratio of hydrogen- to helium-rich objects between 7500 and 6250K, which we interpret as the signature of convective mixing. After this decrease, hydrogen-rich objects become more abundant up to 5000K. This puzzling increase, reminiscent of the non-DA gap, has yet to be explained. At lower temperatures, below 5000K, hydrogen-rich white dwarfs become rarer, which rules out the scenario in which the accretion of hydrogen from the interstellar medium dominates the spectral evolution of cool white dwarfs.
- ID:
- ivo://CDS.VizieR/J/AJ/131/582
- Title:
- Cool white dwarfs in the SDSS
- Short Name:
- J/AJ/131/582
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A reduced proper motion diagram utilising Sloan Digital Sky Survey (SDSS) photometry and astrometry and USNO-B plate astrometry is used to separate cool white dwarf candidates from metal-weak, high-velocity, main-sequence Population II stars (subdwarfs) in the SDSS Data Release 2 imaging area. Follow-up spectroscopy using the Hobby-Eberly Telescope, the MMT, and the McDonald 2.7m telescope is used to demonstrate that the white dwarf and subdwarf loci separate cleanly in the reduced proper motion diagram and that the contamination by subdwarfs is small near the cool white dwarf locus.
- ID:
- ivo://CDS.VizieR/J/AJ/154/72
- Title:
- Coordinates and photometry of stars in Haffner 16
- Short Name:
- J/AJ/154/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Images and spectra recorded with the Gemini Multi-Object Spectrograph on Gemini South are used to investigate the stellar content of the open cluster Haffner 16. The (i',g'-i') color-magnitude diagram (CMD) constructed from these data extends over 10mag in i', sampling the cluster main sequence (MS) and 5mag of the pre-MS (PMS). The fraction of unresolved equal mass binaries among PMS stars is estimated to be 0.6+/-0.1. The isochrones do not track the PMS on the CMD, in the sense that the PMS has a shallower slope on the CMD than predicted by the models. Still, a dip in star counts, which is associated with the relaxation of PMS stars onto the MS, is identified near i'=17. The depth and brightness of this feature-as well as the morphology of the cluster MS on the CMD-are matched by models with a slightly sub-solar metallicity that have an age of ~20Myr and a distance modulus of 12.3+/-0.2. A light profile of Haffner 16 is constructed in the W1 filter ({lambda}_cen_=3.4{mu}m), which suggests that the cluster is surrounded by a diffuse stellar halo. Spectra of candidate cluster MS and PMS stars selected according to location on the CMD are presented. The spectra show characteristics that are suggestive of a sub-solar metallicity. H{alpha} emission is common among objects on the PMS locus on the CMD near i'=18. It is suggested that the location of the Haffner 16 PMS on the CMD is affected by large-scale cool spot activity, likely induced by rapid stellar rotation.
- ID:
- ivo://CDS.VizieR/J/AJ/160/96
- Title:
- CORALIE and PFS radial velocities of HD 86226
- Short Name:
- J/AJ/160/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Transiting Exoplanet Survey Satellite (TESS) mission was designed to find transiting planets around bright, nearby stars. Here, we present the detection and mass measurement of a small, short-period (~4days) transiting planet around the bright (V=7.9), solar-type star HD86226 (TOI-652, TIC22221375), previously known to host a long-period (~1600days) giant planet. HD86226c (TOI-652.01) has a radius of 2.16{+/-}0.08R_{Earth}_ and a mass of 7.25_-1.12_^+1.19^M_{Earth}_, based on archival and new radial velocity data. We also update the parameters of the longer-period, not-known-to-transit planet, and find it to be less eccentric and less massive than previously reported. The density of the transiting planet is 3.97g/cm^3^, which is low enough to suggest that the planet has at least a small volatile envelope, but the mass fractions of rock, iron, and water are not well- constrained. Given the host star brightness, planet period, and location of the planet near both the "radius gap" and the "hot Neptune desert," HD86226c is an interesting candidate for transmission spectroscopy to further refine its composition.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A98
- Title:
- Corona-Australis DANCe. I.
- Short Name:
- J/A+A/634/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photometric data set over a field of 128deg^2^ around the dark clouds of the region. We identify 313 high-probability candidate members to the Corona-Australis association, 262 of which had never been reported as members before. Our sample of members covers the magnitude range between G>~5mag and G<~20mag, and it reveals the existence of two kinematically and spatially distinct subgroups. There is a distributed 'off-cloud' population of stars located in the north of the dark clouds that is twice as numerous as the historically known 'on-cloud' population that is concentrated around the densest cores. By comparing the location of the stars in the HR-diagram with evolutionary models, we show that these two populations are younger than 10Myr. Based on their infrared excess emission, we identify 28 Class II and 215 Class III stars among the sources with available infrared photometry, and we conclude that the frequency of Class~II stars (i.e. `disc-bearing' stars) in the on-cloud region is twice as large as compared to the off-cloud population. The distance derived for the Corona-Australis region based on this updated census is d=149.4^+0.4^_-0.4_pc, which exceeds previous estimates by about 20 pc. In this paper we provide the most complete census of stars in Corona-Australis available to date that can be confirmed with Gaia data. Furthermore, we report on the discovery of an extended and more evolved population of young stars beyond the region of the dark clouds, which was extensively surveyed in the past.
- ID:
- ivo://CDS.VizieR/J/ApJ/896/3
- Title:
- Cosmicflows-4: Tully-Fisher relation calibrations
- Short Name:
- J/ApJ/896/3
- Date:
- 07 Mar 2022 07:21:25
- Publisher:
- CDS
- Description:
- This study is a part of the Cosmicflows-4 project with the aim of measuring the distances of more than ~10000 spiral galaxies in the local universe up to ~15000km/s. New HI line width information has come primarily from the Arecibo Legacy Fast ALFA Survey. Photometry of our sample galaxies has been carried out in optical (SDSS u, g, r, i, and z) and infrared (WISE W1 and W2) bands. Inclinations have been determined using an online graphical interface accessible to a collaboration of citizen scientists. Galaxy distances are measured based on the correlation between the rotation rate of spirals and their absolute luminosity, known as the Tully-Fisher relation (TFR). In this study, we present the calibration of the TFR using a subsample of ~600 spirals located in 20 galaxy clusters. Correlations among such observables as color, surface brightness, and relative HI content are explored in an attempt to reduce the scatter about the TFR with the goal of obtaining more accurate distances. A preliminary determination of the Hubble constant from the distances and velocities of the calibrator clusters is H0=76.0+/-1.1(stat.)+/-2.3(sys.)km/s/Mpc.
