- ID:
- ivo://CDS.VizieR/J/A+A/648/A78
- Title:
- Orphan stream RR Lyrae and non-variables
- Short Name:
- J/A+A/648/A78
- Date:
- 07 Dec 2021 13:05:58
- Publisher:
- CDS
- Description:
- We present a chemo-dynamical study of the Orphan stellar stream using a catalog of RR Lyrae pulsating variable stars for which photometric, astrometric, and spectroscopic data are available. Employing low-resolution spectra from the Sloan Digital Sky Survey (SDSS), we determined line-of-sight velocities for individual exposures and derived the systemic velocities of the RR Lyrae stars. In combination with the stars' spectroscopic metallicities and Gaia EDR3 astrometry, we investigated the northern part of the Orphan stream. In our probabilistic approach, we found 20 single mode RR Lyrae variables likely associated with the Orphan stream based on their positions, proper motions, and distances. The acquired sample permitted us to expand our search to nonvariable stars in the SDSS dataset, utilizing line-of-sight velocities determined by the SDSS. We found 54 additional nonvariable stars linked to the Orphan stream. The metallicity distribution for the identified red giant branch stars and blue horizontal branch stars is, on average, -2.13+/-0.05dex and -1.87+/-0.14dex, with dispersions of 0.23 and 0.43dex, respectively. The metallicity distribution of the RR Lyrae variables peaks at -1.80+/-0.06dex and a dispersion of 0.25dex. Using the collected stellar sample, we investigated a possible link between the ultra-faint dwarf galaxy Grus II and the Orphan stream. Based on their kinematics, we found that both the stream RR Lyrae and Grus II are on a prograde orbit with similar orbital properties, although the large uncertainties on the dynamical properties render an unambiguous claim of connection difficult. At the same time, the chemical analysis strongly weakens the connection between both. We argue that Grus II in combination with the Orphan stream would have to exhibit a strong inverse metallicity gradient, which to date has not been detected in any Local Group system.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/817/1
- Title:
- Palomar/MSU and SDSS-DR7 M dwarfs with GALEX obs.
- Short Name:
- J/ApJ/817/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of Galaxy Evolution Explorer Near-UV (NUV) and Far-UV (FUV) photometry for the Palomar/MSU and SDSS DR7 spectroscopic M dwarf catalogs. The catalog contains NUV measurements matched to 577 spectroscopically confirmed M dwarfs and FUV measurements matched to 150 spectroscopically confirmed M dwarfs. Using these data, we find that NUV and FUV luminosities strongly correlate with H{alpha} emission, a typical indicator of magnetic activity in M dwarfs. We also examine the fraction of M dwarfs with varying degrees of strong line emission at NUV wavelengths. Our results indicate that the frequency of M dwarf NUV emission peaks at intermediate spectral types, with at least ~30% of young M4-M5 dwarfs having some level of activity. For mid-type M dwarfs, we show that NUV emission decreases with distance from the Galactic plane, a proxy for stellar age. Our complete matched source catalog is available online.
- ID:
- ivo://CDS.VizieR/III/198
- Title:
- Palomar/MSU nearby star spectroscopic survey
- Short Name:
- III/198
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Third Catalogue of Nearby Stars (Gliese & Jahreiss, "Preliminary Version of the third Catalogue of Nearby Stars" (CNS3), 1991, catalog <V/70>) includes over 1850 stars which lie north of Dec.= -30{deg} and are either identified as spectral type M, or are unclassified but with an absolute visual magnitude estimate M_V_ > +8.0. Although there is no uniformity in selection criteria, and many of the stars lack basic data (radial velocities, spectral types, accurate photometry), the observational properties of these stars underlie most estimates of the fundamental characteristics of the Galactic Disk. We have obtained optical spectroscopy of 1746 of the 1876 stars -- the remaining 130 are binary companions of brighter stars and inaccessible to our observations. These spectra allow us, first, to exclude 61 stars as either degenerates or as misclassified earlier-type (B-K) stars lying beyond the 25 pc limit; to establish radial velocities accurate to +/-10km/s for all stars confirmed as late-type dwarfs; to determine spectral types and absolute magnitudes from the TiO bandstrength, allowing more accurate distance estimates for stars with inaccurate (or no) trigonometric parallax measurements; and to identify stars with H{alpha} emission (chromospherically active stars) and with strong CaH absorption (perhaps including some metal-poor disk subdwarfs). We have determined the nearby-star luminosity function from complete samples derived by applying both the distance limits defined by Wielen (1974, Highlights of Astron. 3, 395) and by using limits derived from our own analysis. Spectroscopic data for the southern stars (Dec.<-30{deg}) in the PMSU survey are also presented. The data were combined with the data from paper I to obtain a list of all the magnetically active dMe stars in the survey.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A48
- Title:
- Parallaxes for 1146 Pleiades stars
- Short Name:
- J/A+A/598/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distance to the Pleiades open cluster has been extensively debated in the literature over several decades. Although different methods point to a discrepancy in the trigonometric parallaxes produced by the Hipparcos mission, the number of individual stars with known distances is still small compared to the number of cluster members to help solve this problem. We provide a new distance estimate for the Pleiades based on the moving cluster method, which will be useful to further discuss the so-called Pleiades distance controversy and compare it with the very precise parallaxes from the Gaia space mission. We apply a refurbished implementation of the convergent point search method to an updated census of Pleiades stars to calculate the convergent point position of the cluster from stellar proper motions. Then, we derive individual parallaxes for 64 cluster members using radial velocities compiled from the literature, and approximate parallaxes for another 1146 stars based on the spatial velocity of the cluster. This represents the largest sample of Pleiades stars with individual distances to date. The parallaxes derived in this work are in good agreement with previous results obtained in different studies (excluding Hipparcos) for individual stars in the cluster. We report a mean parallax of 7.44+/-0.08mas and distance of 134.4^+2.9^_-2.8_pc that is consistent with the weighted mean of 135.0+/-0.6pc obtained from the non-Hipparcos results in the literature. Our result for the distance to the Pleiades open cluster is not consistent with the Hipparcos catalog, but favors the recent and more precise distance determination of 136.2+/-1.2pc pc obtained from Very Long Baseline Interferometry observations. It is also in good agreement with the mean distance of 133+/-5pc obtained from the first trigonometric parallaxes delivered by the Gaia satellite for the brightest cluster members in common with our sample.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A20
- Title:
- Parallax zero-point offset from Gaia EDR3 data
- Short Name:
- J/A+A/654/A20
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The second data release of Gaia revealed a parallax zero-point offset of -0.029mas based on quasars. The value depended on the position on the sky, and also likely on magnitude and colour. The offset and its dependence on other parameters inhibited improvement in the local distance scale using for example the Cepheid and RR Lyrae period-luminosity relations. Analysis of the recent Gaia Early Data Release 3 (EDR3) reveals a mean parallax zero-point offset of -0.021 mas based on quasars. The Gaia team addresses the parallax zero-point offset in detail and proposes a recipe to correct for it based on ecliptic latitude, G-band magnitude, and colour information. This paper presents a completely independent investigation into this issue focusing on the spatial dependence of the correction based on quasars and the magnitude dependence based on wide binaries. The spatial and magnitude corrections are connected to each other in the overlap region in the range 17<G<19. The spatial correction is presented at several spatial resolutions based on the HEALPix formalism. The colour dependence of the parallax offset is unclear and in any case secondary to the spatial and magnitude dependence. The spatial and magnitude corrections are applied to two samples of brighter sources, namely a sample of approximately 100 stars with independent trigonometric parallax measurements from Hubble Space Telescope data, and a sample of 75 classical cepheids using photometric parallaxes. The mean offset between the observed GEDR3 parallax and the independent trigonometric parallax (excluding outliers) is about -39{mu}as, and after applying the correction it is consistent with being zero. For the classical cepheid sample the analysis presented here suggests that the photometric parallaxes may be underestimated by about 5%.
- ID:
- ivo://CDS.VizieR/J/A+A/466/627
- Title:
- Parameters of DA white dwarfs in SDSS-DR1
- Short Name:
- J/A+A/466/627
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The SDSS Data Release 1 includes 1833 DA white dwarfs (WDs) and forms the largest homogeneous sample of WDs. This sample provides the best opportunity to study the statistical properties of WDs. We adopt a recently established theoretical model to calculate the mass and distance of each WD using the observational data. Then we adopt a bin-correction method to correct for selection effects and use the 1/V weight-factor method to calculate the luminosity function, the continuous mass function and the formation rate of these WDs.
- ID:
- ivo://CDS.VizieR/J/AJ/158/73
- Title:
- Parameters of OB stars & their bow shock nebulae
- Short Name:
- J/AJ/158/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Motivated by the need to reconcile observational values and theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of OB stars that generate bow shock nebulae. We measure peculiar velocities from new Gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected bow shock nebulae, 67 are OB stars. The median peculiar velocity is 11 km/s, significantly smaller than classical "runaway star" velocities. Mass-loss rates for these O and early B stars agree with recently lowered theoretical predictions, ranging from ~10^-7^ M_{sun}_/yr for mid-O dwarfs to 10^-9^ M_{sun}_/yr for late O dwarfs - a factor of about 2.7 lower than the often-used Vink et al. (2000A&A...362..295V, 2001A&A...369..574V) formulation. Our results provide the first observational mass-loss rates for B0-B3 dwarfs and giants - 10^-9^ to 10^-8^ M_{sun}_/yr. We find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bistability phenomenon in the range T_eff_=19000-27000 K. The sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical wind-luminosity relations. We identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. For these, the inferred mass-loss rates must be regarded as upper limits.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/L26
- Title:
- Parameters of radio sources near Sgr A*
- Short Name:
- J/ApJ/801/L26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radio images within 30" of Sgr A* based on recent VLA observations at 34 GHz with 7.8 {mu}Jy sensitivity and resolution of ~88x46 mas. We report 44 partially resolved compact sources clustered in two regions in the E arm of ionized gas that orbits Sgr A*. These sources have size scales ranging between ~50 and 200 mas (400-1600 AUs), and a bow-shock appearance facing the direction of Sgr A*. Unlike the bow-shock sources previously identified in the near-IR but associated with massive stars, these 34 GHz sources do not appear to have near-IR counterparts at 3.8 {mu}m. We interpret these sources as a candidate population of photoevaporative protoplanetary disks (proplyds) that are associated with newly formed low mass stars with mass loss rates ~10^-7^-10^-6^ M_{sun}_/yr and are located at the edge of a molecular cloud outlined by ionized gas. The disks are externally illuminated by strong Lyman continuum radiation from the ~100 OB and WR massive stars distributed within 10" of Sgr A*. The presence of proplyds implies current in situ star formation activity near Sgr A* and opens a window for the first time to study low mass star, planetary, and brown dwarf formations near a supermassive black hole. The video abstract was created from a WorldWide Telescope tour file, which is available for download. Viewing the file requires a Windows PC with the WorldWide Telescope desktop client available at worldwidetelescope.org.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/2295
- Title:
- 25 parsec local white dwarf population
- Short Name:
- J/MNRAS/462/2295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have extended our detailed survey of the local white dwarf population from 20 to 25pc, effectively doubling the sample volume, which now includes 232 stars. In the process, new stars within 20 pc have been added, a more uniform set of distance estimates as well as improved spectral and binary classifications are available. The present 25pc sample is estimated to be about 68 per cent complete (the corresponding 20pc sample is now 86 per cent complete). The space density of white dwarfs is unchanged at 4.8+/-0.5x10^-3^pc^-3^. This new study includes a white dwarf mass distribution and luminosity function based on the 232 stars in the 25pc sample. We find a significant excess of single stars over systems containing one or more companions (74 per cent versus 26 per cent). This suggests mechanisms that result in the loss of companions during binary system evolution. In addition, this updated sample exhibits a pronounced deficiency of nearby 'Sirius-like' systems. 11 such systems were found within the 20pc volume versus only one additional system found in the volume between 20 and 25pc. An estimate of white dwarf birth rates during the last ~8Gyr is derived from individual remnant cooling ages. A discussion of likely ways new members of the local sample may be found is provided.
- ID:
- ivo://CDS.VizieR/J/ApJ/808/194
- Title:
- Performance of exoplanet search space missions
- Short Name:
- J/ApJ/808/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analytic model to estimate the capabilities of space missions dedicated to the search for biosignatures in the atmosphere of rocky planets located in the habitable zone of nearby stars. Relations between performance and mission parameters, such as mirror diameter, distance to targets, and radius of planets, are obtained. Two types of instruments are considered: coronagraphs observing in the visible, and nulling interferometers in the thermal infrared. Missions considered are: single-pupil coronagraphs with a 2.4m primary mirror, and formation-flying interferometers with 4x0.75m collecting mirrors. The numbers of accessible planets are calculated as a function of {eta}_Earth_. When Kepler gives its final estimation for {eta}_Earth_, the model will permit a precise assessment of the potential of each instrument. Based on current estimations, {eta}_Earth_=10% around FGK stars and 50% around M stars, the coronagraph could study in spectroscopy only ~1.5 relevant planets, and the interferometer ~14.0. These numbers are obtained under the major hypothesis that the exozodiacal light around the target stars is low enough for each instrument. In both cases, a prior detection of planets is assumed and a target list established. For the long-term future, building both types of spectroscopic instruments, and using them on the same targets, will be the optimal solution because they provide complementary information. But as a first affordable space mission, the interferometer looks the more promising in terms of biosignature harvest.
