- ID:
- ivo://CDS.VizieR/J/AJ/124/1670
- Title:
- Post-T Tauri Stars in Sco-Cen Association
- Short Name:
- J/AJ/124/1670
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a spectroscopic survey of X-ray and proper-motion-selected samples of late-type stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) subgroups of the nearest OB association: Scorpius-Centaurus. The primary goals of the survey are to determine the star formation history of the OB subgroups and to assess the frequency of accreting stars in a sample dominated by "post-T Tauri" pre-main-sequence (PMS) stars. We investigate two samples: (1) proper-motion candidates from the ACT Catalog (<I/246>) and Tycho Reference Catalog (TRC, <I/250>) with X-ray counterparts in the ROSAT All-Sky Survey (RASS) Bright Source Catalog and (2) G- and K-type stars in the Hipparcos catalog found to be candidate members by de Zeeuw et al. (1999, Cat. <J/AJ/117/354>). We obtained optical spectra of 130 candidates with the Siding Spring 2.3m dual-beam spectrograph.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/523/A23
- Title:
- Properties of OB associations in IC 1613
- Short Name:
- J/A+A/523/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the structure and evolution of massive stars, systematic surveys of the Local Group galaxies have been undertaken, to find these objects in environments of different chemical abundances. We focus on the metal-poor irregular galaxy IC 1613 to analyze the stellar and wind structure of its low-metallicity massive stars. We ultimately aim to study the metallicity-dependent driving mechanism of the winds of blue massive stars and use metal-poor massive stars of the Local Volume as a proxy for the stars in the early Universe. In a previous paper we produced a list of OB associations in IC 1613. Their properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the structure and recent star formation history of the galaxy. We characterize these OB associations and study their connection with the galactic global properties. The reddening-free Q parameter is a powerful tool in the photometric analysis of young populations of massive stars, since it exhibits a smaller degree of degeneracy with OB spectral types than the B-V color. The color-magnitude diagram (Q vs. V) of the OB associations in IC 1613 is studied to determine their age and mass, and confirm the population of young massive stars. We identified more than 10 stars with M>=50M_{sun}_. Spectral classification available for some of them confirm their massive nature, yet we find the common discrepancy with the spectroscopically derived masses. There is a general increasing trend of the mass of the most massive member with the number of members of each association, but not with the stellar density. The average diameter of the associations of this catalog is 40pc, half the historically considered typical size of OB associations. Size increases with the association population. The distribution of the groups strongly correlates with that of neutral and ionized hydrogen. We find the largest dispersion of association ages in the bubble region of the galaxy where hydrogen is abundant, implying that recent star formation has proceeded over a longer period of time than in the rest of the galaxy, and is still ongoing. Very young associations are found at the west of the galaxy far from the bubble region, traditionally considered the sole locus of star formation, but still rich in neutral hydrogen. The contrast in the stellar properties derived from photometry and spectroscopy (when the latter is available) shows that the Q pseudo-color is very useful for estimating the parameters of OB stars when only photometric observations exist. This work helped define an extensive pool of candidate OB stars for subsequent spectroscopic analyses designed to study the structure and winds of metal-poor massive stars.
- ID:
- ivo://CDS.VizieR/J/A+A/377/925
- Title:
- Radial velocity curves of Vela X-1
- Short Name:
- J/A+A/377/925
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper the mass of the neutron star in Vela X-1 is determined, by measuring the radial velocity curve of its B supergiant companion. The tables (appendix of the paper), which list the log of observations, and the derived radial velocities, of the blue Coude Echelle Spectrograph (CES) spectra (Table A1), the red CES spectra (Table A2), and the IUE spectra (Table A3).
- ID:
- ivo://CDS.VizieR/J/A+A/281/161
- Title:
- Radio emission from stars at 250GHz
- Short Name:
- J/A+A/281/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the IRAM 30 m-telescope together with the Max Planck Institute for Radio Astronomy (MPIfR) bolometer to survey nearly 270 stars of different types for 250GHz continuum emission. We compare these data with their low frequency (cm-range) properties. Early type stars show very often a deviation from the uniformly expanding wind model which we tentatively attribute to temperature and/or density fluctuations in their deeper atmospheric layers. For WR stars this deviation seems to depend on the effective temperature. Pre-main sequence stars usually seem to be surrounded by a shell of warm dust making a substantial contribution to the 250 GHz flux density value. We have found especially for nearby giants and supergiants that a layer at the transition from photosphere to chromosphere emits ample 250 GHz radiation. We show that the present data can still be explained by a simple uniformly illuminated disk model with the known stellar radius. Optically variable stars are not very strong emitters at 250 GHz. We preferentially detected the more exotic ones, a few Beta Lyr-type and symbiotic stars. Comments on many individual objects are given in the appropriate sections.
- ID:
- ivo://CDS.VizieR/J/MNRAS/508/2370
- Title:
- Revisiting the Cygnus OB associations
- Short Name:
- J/MNRAS/508/2370
- Date:
- 24 Jan 2022 09:16:32
- Publisher:
- CDS
- Description:
- OB associations play an important role in Galactic evolution, though their origins and dynamics remain poorly studied, with only a small number of systems analysed in detail. In this paper we revisit the existence and membership of the Cygnus OB associations. We find that of the historical OB associations only Cyg OB2 and OB3 stand out as real groups. We search for new OB stars using a combination of photometry, astrometry, evolutionary models and an SED fitting process, identifying 4680 probable OB stars with a reliability of >90%. From this sample we search for OB associations using a new and flexible clustering technique, identifying 6 new OB associations. Two of these are similar to the associations Cyg OB2 and OB3, though the others bear no relationship to any existing systems. We characterize the properties of the new associations, including their velocity dispersions and total stellar masses, all of which are consistent with typical values for OB associations. We search for evidence of expansion and find that all are expanding, albeit anistropically, with stronger and more significant expansion in the direction of Galactic longitude. We also identify two large-scale (160pc and 25km/s) kinematic expansion patterns across the Cygnus region, each including three of our new associations, and attribute this to the effects of feedback from a previous generation of stars. This work highlights the need to revisit the existence and membership of the historical OB associations, if they are to be used to study their properties and dynamics.
- ID:
- ivo://CDS.VizieR/J/A+AS/118/481
- Title:
- ROSAT all-sky survey catalogue of OB stars
- Short Name:
- J/A+AS/118/481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the detailed statistical analysis of the X-ray emission of hot stars we selected all stars of spectral type O and B listed in the Yale Bright Star Catalogue and searched for them in the ROSAT All-Sky Survey. In this paper we describe the selection and preparation of the data and present a compilation of the derived X-ray data for a complete sample of bright OB stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/284/265
- Title:
- Rotational Velocities of 373 OB stars
- Short Name:
- J/MNRAS/284/265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of homogeneous measures of the linewidth parameter, v_e_.sin(i), for 373 O-type stars and early supergiants (including the separate components of 25 binary and triple systems), produced by cross-correlating high-resolution, short-wavelength IUE spectra against a `template' spectrum of {tau} Sco. We also tabulate terminal velocities. There are no O supergiants in our sample with v_e_.sin(i)<65km/s, and only one supergiant earlier than B5 has v_e_.sin(i)<50km/s, confirming that an important line broadening mechanism in addition to rotation must be present in these objects. A calibration of the area under the cross-correlation peak against spectral type is used to obtain estimates of continuum intensity ratios of the components in 28 spectroscopically binary or multiple systems. At least seven SB2 systems show evidence for the `Struve-Sahade effect', a systematic variation in relative line strength as a function of orbital phase. The stellar wind of the most rapid rotator in our sample, the O9III:n* star HD 191423 (v_e_.sin(i)<=436km/s), show it to have a `wind-compressed disc' similar to that of HD 93521; this star and other rapid rotators are good candidates for studies of non-radial pulsation.
- ID:
- ivo://CDS.VizieR/J/AJ/134/1570
- Title:
- Rotational velocities of OB stars
- Short Name:
- J/AJ/134/1570
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive projected rotational velocities (vsini) for a sample of 156 Galactic OB star members of 35 clusters, HII regions, and associations. The HeI lines at 4026, 4388, and 4471{AA} were analyzed in order to define a calibration of the synthetic HeI full widths at half-maximum (FWHMs) versus stellar vsini. A grid of synthetic spectra of HeI line profiles was calculated in non-LTE using an extensive helium model atom and updated atomic data. The vsini values for all stars were derived using the HeI FWHM calibrations, but also, for those target stars with relatively sharp lines, vsini values were obtained from best-fit synthetic spectra of up to 40 lines of CII, NII, OII, AlIII, MgII, SiIII, and SIII. This calibration is a useful and efficient tool for estimating the projected rotational velocities of O9-B5 main-sequence stars. The distribution of vsini for an unbiased sample of early B stars in the unbound association Cep OB2 is consistent with the distribution reported elsewhere for other unbound associations.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/844
- Title:
- Rotation rates of very massive stars
- Short Name:
- J/ApJ/700/844
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present projected rotational velocity values for 96 Galactic, 55 SMC, and 106 LMC O-B type stars from archival FUSE observations. The evolved and unevolved samples from each environment are compared through the Kolmogorov-Smirnov test to determine if the distribution of equatorial rotational velocities is metallicity dependent for these massive objects. Stellar interior models predict that massive stars with SMC metallicity will have significantly reduced angular momentum loss on the main sequence compared to their Galactic counterparts. Our results find some support for this prediction but also show that even at Galactic metallicity, evolved and unevolved massive stars have fairly similar fractions of stars with large Vsin i values. Macroturbulent broadening that is present in the spectral features of Galactic evolved massive stars is lower in the LMC and SMC samples. This suggests the processes that lead to macroturbulence are dependent upon metallicity.
- ID:
- ivo://CDS.VizieR/J/AJ/156/98
- Title:
- Runaway stars in the 30 Doradus region of the LMC
- Short Name:
- J/AJ/156/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of relative proper motions for 368787 stars in the 30 Doradus region of the Large Magellanic Cloud (LMC), based on a dedicated two-epoch survey with the Hubble Space Telescope and supplemented with proper motions from our pilot archival study. We demonstrate that a relatively short epoch difference of three years is sufficient to reach a level of precision of ~0.1 mas/yr or better. A number of stars with relative proper motions exceeding a 3{sigma} error threshold represent a mixture of Milky Way denizens and 18 potential LMC runaway stars. Based upon 183 VFTS OB stars with the best proper motions, we conclude that none of them moves faster than ~0.3 mas/yr in each coordinate-equivalent to ~70 km/s. Among the remaining 351 VFTS stars with less accurate proper motions, only one candidate OB runaway can be identified. We rule out any OB star in our sample moving at a tangential velocity exceeding ~120 km/s. The most significant result of this study is finding 10 stars over a wide range of masses that appear to have been ejected from the massive star cluster R136 in the tangential plane to angular distances from 35" out to 407", equivalent to 8-98 pc. The tangential velocities of these runaways appear to be correlated with apparent magnitude, indicating a possible dependence on the stellar mass. Lastly, a comparison to proper motions from Gaia DR 2 shows that for several relatively bright stars the DR 2 has an unexpected scatter that cannot be accounted for by the formal errors.
