- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/135/1225
- Title:
- Parameters of the local white dwarfs
- Short Name:
- J/AJ/135/1225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a detailed new survey of the local population of white dwarfs lying within 20pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20pc sample is currently estimated to be 80% complete. Using a variety of recent spectroscopic, photometric, and trigonometric distance determinations, we re-compute a space density of 4.8+/-0.5x10^-3^pc^-3^ corresponding to a mass density of 3.2+/-0.3x10^-3^M_{sun}_pc^-3^ from the complete portion of the sample within 13pc. We find an overall mean mass for the local white dwarfs of 0.665M_{sun}_, a value larger than most other non-volume-limited estimates. Although the sample is small, we find no evidence of a correlation between mass and temperature in which white dwarfs below 13000K are systematically more massive than those above this temperature. Within 20pc 25% of the white dwarfs are in binary systems (including double degenerate systems). Approximately 6% are double degenerates and 6.5% are Sirius-like systems. The fraction of magnetic white dwarfs in the local population is found to be 13%.
- 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.
- ID:
- ivo://CDS.VizieR/III/150A
- Title:
- Perkins Revised MK Types for the Cooler Stars
- Short Name:
- III/150A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The original catalog of standard stars classified on the Revised MK system published in 1989 contains 1054 standard stars of spectral types G0 and later (G, K, M, and a few S stars) classified at the Perkins Observatory. The present version of the catalog takes into account the revisions (before 14h of RA) presented by Philip C. Keenan and Gerald H. Newsom at the Department of Astronomy of the Ohio State University (http://www-astronomy.mps.ohio-state.edu/MKCool) dated 2000 January; the Sun (G2V star) has been omitted from the catalog. Accurate positions were added in 2003. The revised MK system is described by Keenan (1987PASP...99..713K). The spectrograms used for the classification were taken at four different observatories; hence, extensive comparisons have been made to ensure consistency between the Northern and Southern Hemispheres. The list provides a consistent set of standards in most parts of the sky and over a considerable range in magnitude, for stars later than G0. The catalog is not a survey complete to any magnitude and is not intended for statistical studies.
- ID:
- ivo://CDS.VizieR/J/AJ/153/252
- Title:
- Photometric variability of BeSS-KELT stars
- Short Name:
- J/AJ/153/252
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10 years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.
- ID:
- ivo://CDS.VizieR/J/A+A/532/A103
- Title:
- Photometry and proper motions in IC4665
- Short Name:
- J/A+A/532/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the mass function in open clusters constitutes one way to constrain the formation of low-mass stars and brown dwarfs along with the knowledge of the frequency of multiple systems and the properties of disks. The aim of the project is to determine the shape of the mass function in the low-mass and substellar regimes in the pre-main sequence (27Myr) cluster IC4665 located at 350pc from the Sun. We have cross-matched the near-infrared photometric data from the Eighth Data Release (DR8) of the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) with previous optical data obtained with the Canada-France-Hawaii (CFH) wide-field camera to improve the determination of the luminosity and mass functions in the low-mass and substellar regimes. The availability of i and z photometry taken with the CFH12K camera on the Canada France Hawaii Telescope added strong constraints to the UKIDSS photometric selection in this cluster located in a dense region of our Galaxy. We have derived the luminosity and mass functions of the cluster down to J=18.5mag, corresponding to masses of ~0.025M_{sun}_ at the distance and age of IC4665 according to theoretical models. In addition, we have extracted new candidate members down to ~20 Jupiter masses in a previously unstudied region of the cluster. We have derived the mass function over the 0.6-0.04M_{sun}_ mass range and found that it is best represented by a log-normal function with a peak at 0.25-0.16M_{sun}_, consistent with the determination in the Pleiades.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/1484
- Title:
- Photometry and spectroscopy in IC 2391
- Short Name:
- J/ApJ/706/1484
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar and substellar mass function (MF) of the open cluster IC 2391, plus its radial dependence, and use this to put constraints on the formation mechanism of brown dwarfs (BDs). Our multi-band optical and infrared photometric survey with spectroscopic follow-up covers 11deg^2^, making it the largest survey of this cluster to date. From our preliminary spectroscopic follow-up, to confirm BD status and cluster membership, we find that all candidates are M dwarfs (in either the field or the cluster), demonstrating the efficiency of our photometric selection method in avoiding contaminants (e.g., red giants). About half of our photometric candidates for which we have spectra are spectroscopically confirmed as cluster members; two are new spectroscopically confirmed BD members of IC 2391.
- ID:
- ivo://CDS.VizieR/J/BaltA/18/33
- Title:
- Photometry of stars around NGC 7023
- Short Name:
- J/BaltA/18/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interstellar extinction is investigated in a 1.5 square degree area in the direction of the reflection nebula NGC7023 at l=104.1{deg}, b=+14.2{deg}. The study is based on photometric classification and the determination of interstellar extinctions and distances of 480 stars down to V=16.5mag from photometry in the Vilnius seven-color system published in Paper I (2008BaltA..17..161Z). The investigated area is divided into five smaller subareas with slightly different dependence of the extinction on distance. The distribution of reddened stars is in accordance with the presence of two dust clouds at 282pc and 715pc, however in some directions the dust distribution can be continuous or more clouds can be present.
259. Photometry of W UMa
- ID:
- ivo://CDS.VizieR/J/A+A/311/523
- Title:
- Photometry of W UMa
- Short Name:
- J/A+A/311/523
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The physical properties of W UMa binary systems are revisited on the basis of the observational data published in the last decade and of the recent theoretical studies on angular-momentum-loss-driven secular evolution. The absolute elements (masses, radii, luminosities) are derived by an inference method and a calibration based on the available high quality spectroscopic orbits. The derived age (8Gy) agrees with the estimate of Guinan and Bradstreet from space motions. The analysis of the resulting physical parameters shows little correlation between the standard classification in A and W subtype (first proposed by Binnendijk (1970) and only related to the light curve morphology) and the evolutionary status and origin of the systems. Most A-subtype systems seem to have no evolutionary link with W-subtype ones. The relation between total mass and mass ratio for the "bona fide" sample also suggests that mass loss from the system may play an important role.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/97
- Title:
- Photospheric properties of T Tauri stars
- Short Name:
- J/ApJ/786/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.
