- ID:
- ivo://CDS.VizieR/J/A+A/540/A57
- Title:
- Mass function of Quintuplet cluster
- Short Name:
- J/A+A/540/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar mass function is a probe for a potential dependence of star formation on the environment. Only a few young clusters are known to reside within the central molecular zone and can serve as test-beds for star formation under the extreme conditions in this region. We determine the present-day mass function of the Quintuplet cluster, a young massive cluster in the vicinity of the Galactic centre. We use two epochs of high resolution near infrared imaging data obtained with NAOS/CONICA at the ESO VLT to measure the individual proper motions of stars in the Quintuplet cluster in the cluster reference frame. An unbiased sample of cluster members within a radius of 0.5pc from the cluster centre was established based on their common motion with respect to the field and a subsequent colour-cut. Initial stellar masses were inferred from four isochrones covering ages from 3 to 5Myr and two sets of stellar evolution models. For each isochrone, the present-day mass function of stars was determined for the full sample of main sequence cluster members using an equal number binning scheme. We find the slope of the present-day mass function in the central part of the Quintuplet cluster to be alpha=-1.68^+0.13^_-0.09_ for an approximate mass range from 5 to 40M_{sun}_, which is significantly flatter than the Salpeter slope of alpha=-2.35. The flattening of the present-day mass function may be caused by rapid dynamical evolution of the cluster in the strong Galactic centre tidal field. The derived mass function slope is compared to the values found in other young massive clusters in the Galaxy.
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- ID:
- ivo://CDS.VizieR/J/A+A/597/A22
- Title:
- Massive O- and B-type stars velocities
- Short Name:
- J/A+A/597/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The term macroturbulent broadening is commonly used to refer to a certain type of non-rotational broadening acting the spectral line profiles of O- and B-type stars. It has been proposed to be a spectroscopic signature of the presence of stellar oscillations; however, we still lack a definitive confirmation of this hypothesis. We aim to provide new empirical clues about macroturbulent spectral line broadening in O- and B-type stars to evaluate its physical origin. We used high-resolution spectra of 430 stars with spectral types in the range O4-B9 (all luminosity classes) compiled in the framework of the IACOB project. We characterized the line broadening of adequate diagnostic metal lines using a combined Fourier transform and goodness-of-fit technique. We performed a quantitative spectroscopic analysis of the whole sample using automatic tools coupled with a huge grid of FASTWIND models to determine their effective temperatures and gravities. We also incorporated quantitative information about line asymmetries into our observational description of the characteristics of the line profiles, and performed a comparison of the shape and type of line-profile variability found in a small sample of O stars and B supergiants with still undefined pulsational properties and B main-sequence stars with variable line profiles owing to a well-identified type of stellar oscillations or to the presence of spots in the stellar surface.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A157
- Title:
- Massive O-type stars near ZAMS elusive detection
- Short Name:
- J/A+A/638/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The apparent lack of massive O-type stars near the Zero Age Main Sequence, or ZAMS, (at ages <2Myr) has been a topic widely discussed in the last 40 years. Different explanations for the elusive detection of these young massive stars have been proposed from both the observational and theoretical side, but no firm conclusions have been reached yet. The aim of this work is to perform a reassessment of this empirical result benefiting from the high quality spectroscopic observations of (more than 400) Galactic O-type stars gathered by the IACOB and OWN surveys. We use effective temperatures and surface gravities resulting from a homogeneous, semi-automatized, IACOB-GBAT/FASTWIND spectroscopic analysis to locate our sample of stars in the Kiel and spectroscopic Hertzsprung-Russell (HR) diagrams. We evaluate the completeness of our magnitude limited sample of stars - as well as the existence of potential observational biases affecting the compiled sample - using information from the Galactic O star catalog (GOSC). We discuss limitations and possible systematics of our analysis methodology, and compare our results with other recent studies using smaller samples of Galactic O-type stars. We mainly base our discussion on the distribution of stars in the spectroscopic HR diagram in order to avoid the use of still uncertain distances to most of the stars in our sample. However, we also perform a more detailed study of the young cluster Trumpler-14 as an illustrative example of how Gaia cluster distances can help to construct the associated classical HR diagram. We find that the apparent lack of massive O-type stars near the zero-age main sequence with initial evolutionary masses in the range between ~30 and 70M_{sun}_ still persist despite using spectroscopic results from a large, non-biased sample of stars. We do not find any correlations between the dearth of stars close to the ZAMS and obvious observational biases, limitations of our analysis methodology, and/or the use of one example spectroscopic HR diagram instead of the classical one. Finally, by investigating the impact of the efficiency of mass accretion during the formation process of massive stars, we conclude that an adjustment of the mass accretion rate towards lower values than canonically assumed could reconcile the hotter boundary of the empirical distribution of optically detected O-type stars in the spectroscopic HR diagram and the theoretical birthline for stars with masses above 30M_{sun}_. Last, we also discuss how the presence of a small sample of O2-O3.5 stars found much closer to the ZAMS than the main distribution of Galactic O-type star could be explained in the context of this scenario taking also into account the effect of non-standard star evolution (e.g. binary interaction, mergers, and/or homogeneous evolution).
- ID:
- ivo://CDS.VizieR/J/AJ/126/1455
- Title:
- 2MASS photometry of hot subdwarf stars
- Short Name:
- J/AJ/126/1455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Utilizing the Two Micron All Sky Survey (2MASS) Second Incremental Data Release Catalog, we have retrieved near-IR magnitudes for several hundred hot subdwarfs (sdO and sdB stars) drawn from the Catalogue of Spectroscopically Identified Hot Subdwarfs by Kilkenny et al. (1988SAAOC..12....1K). This sample size greatly exceeds that of previous studies of hot subdwarfs. Examining 2MASS photometry alone or in combination with visual photometry (Johnson BV or Stroemgren uvby) available in the literature, we show that it is possible to identify hot subdwarf stars that exhibit atypically red IR colors, which can be attributed to the presence of an unresolved late-type companion. Utilizing this large sample, we attempt for the first time to define an approximately volume-limited sample of hot subdwarfs. We discuss the considerations, biases, and difficulties in defining such a sample. We find that, of the hot subdwarfs in Kilkenny et al. (1988SAAOC..12....1K), about 40% in a magnitude-limited sample have colors that are consistent with the presence of an unresolved late-type companion. Binary stars are overrepresented in a magnitude-limited sample. In an approximately volume-limited sample the fraction of composite-color binaries is about 30%.
- ID:
- ivo://CDS.VizieR/J/A+A/404/689
- Title:
- Metallicities of Slowly Pulsating B stars
- Short Name:
- J/A+A/404/689
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived the stellar parameters (angular diameters, effective temperatures, metallicities) and interstellar reddenings for 20 Slowly Pulsating B (SPB) and 34 reference stars observed during the IUE satellite mission. The parameters were derived by means of an algorithmic procedure of fitting theoretical flux distributions to the low-resolution IUE spectra and optical spectrophotometric observations. Since the metallicity [m/H] has a special importance for pulsating B type stars, we focused our attention on that parameter. We found that the mean value of the metallicity of the considered SPB and reference stars amounts to [m/H]~-0.20. The results only slightly depend on the reduction procedure used for the IUE images (NEWSIPS and INES). The metal abundances obtained in this paper are in accordance with the average value of -0.2dex for stars in the solar neighborhood recently reported by other investigators.
- ID:
- ivo://CDS.VizieR/J/MNRAS/371/1793
- Title:
- Metallicity calibrations for UBV photometry
- Short Name:
- J/MNRAS/371/1793
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Calibrations are presented here for metallicity ([Fe/H]) in terms of the ultraviolet excess, [{Delta}(U-B) at B-V=0.6, hereafter D0.6], and also for the absolute visual magnitude (M_V_) and its difference with respect to the Hyades ({Delta}M^H^_V_) in terms of D0.6 and (B-V), making use of high-resolution spectroscopic abundances from the literature and Hipparcos parallaxes.
- ID:
- ivo://CDS.VizieR/J/AJ/106/1839
- Title:
- Metal-rich halo A stars
- Short Name:
- J/AJ/106/1839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of spectrophotometry of the Ca II K and Balmer lines and radial velocity measurements for stars earlier than type F0, with 10<V<15.5 in fields at (l;b)=(90deg, 270deg; -45deg) are reported. Slit spectroscopy of 320 stars shows that in this magnitude range there are ~80 stars with [Fe/H]>-0.5. The metal-rich population has a vertical scale height of ~600pc and a space density at the Sun equal to 1/225 of the young thin disk A star population. The metal-rich A stars have V_rot_=210+/-60km/s with decreasing angular momentum as a function of distance from the Galactic plane. The line-of-sight velocity dispersion is 40+/-3km/s indicating an anomalous relation between structure and kinematics. There is strong evidence that these stars are identical in properties to the metal-rich extended populations found by Perry [1969AJ.....74..139P] at the NGP and Rodgers [1971ApJ...165..581R] at the SGP.
- ID:
- ivo://CDS.VizieR/J/AJ/139/59
- Title:
- Milky Way halo velocity dispersion profile
- Short Name:
- J/AJ/139/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic sample of 910 distant halo stars from the Hypervelocity Star survey from which we derive the velocity dispersion profile of the Milky Way halo. The sample is a mix of 74% evolved horizontal branch stars and 26% blue stragglers. We estimate distances to the stars using observed colors, metallicities, and stellar evolution tracks. Our sample contains twice as many objects with R>50kpc as previous surveys. We compute the velocity dispersion profile in two ways: with a parametric method based on a Milky Way potential model and with a non-parametric method based on the caustic technique originally developed to measure galaxy cluster mass profiles. The resulting velocity dispersion profiles are remarkably consistent with those found by two independent surveys based on other stellar populations: the Milky Way halo exhibits a mean decline in radial velocity dispersion of -0.38+/-0.12km/s/kpc over 15<R<75kpc. This measurement is a useful basis for calculating the total mass and mass distribution of the Milky Way halo.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/2432
- Title:
- MiMeS magnetic analysis of O-type stars
- Short Name:
- J/MNRAS/465/2432
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the Magnetism in Massive Stars (MiMeS) Survey. Mean least-squares deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field B_l_. The investigation of the Stokes I profiles led to the discovery of two new multiline spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041. We present a modified strategy of the least-squares deconvolution technique aimed at optimizing the detection of magnetic signatures while minimizing the detection of spurious signatures in Stokes V. Using this analysis, we confirm the detection of a magnetic field in six targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in three new magnetic candidates (HD 36486, HD 162978, and HD 199579). Overall, we find a magnetic incidence rate of 7+/-3 per cent, for 108 individual O stars (including all O-type components part of multiline systems), with a median uncertainty of the B_l_ measurements of about 50G. An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars. Similar to A- and B-type stars, we find no link between the stars' physical properties (e.g. T_eff_, mass, and age) and the presence of a magnetic field. However, the Of?p stars represent a distinct class of magnetic O-type stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/2
- Title:
- MiMeS survey of magnetism in massive stars
- Short Name:
- J/MNRAS/456/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada-France-Hawaii Telescope, Narval at the Telescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6m telescope, making MiMeS by far the largest systematic investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole fields above approximately 100G, discuss the polarimetric performance, stability and uncertainty of the instrumentation, and summarize the previous and forthcoming publications.
