- ID:
- ivo://CDS.VizieR/J/ApJ/704/964
- Title:
- Spectroscopic study of Of^+^ supergiants
- Short Name:
- J/ApJ/704/964
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The transition from early Of stars to WN-type objects is poorly understood. O-type supergiants with emission lines (OIf^+^) are considered to be intermediate between these two classes. The scope of this paper is to investigate the spectral variability of three Of^+^ supergiants. We constituted spectral time series of unprecedented quality for our targets (~200 spectra in total), essentially in the blue domain, covering timescales from a few hours up to a few years. Temporal Variance Spectrum and Fourier analyses were performed in order to characterize their spectral variability.
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- ID:
- ivo://CDS.VizieR/J/other/RAA/18.146
- Title:
- Spiral structure of the Milky Way
- Short Name:
- J/other/RAA/18.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics. In this review we firstly summarize various methods with different tracers used to solve this puzzle. The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes (a few {mu}as) and proper motions (~1km/s) by using Very Long Baseline Interferometry (VLBI). On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way. Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail. Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center, R_0_, to be 8.35+/-0.18kpc, and circular rotation speed at the Sun, {THETA}_0_, to be 240+/-10km/s. We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster, >8km/s than maser-traced high-mass star forming regions.
- ID:
- ivo://CDS.VizieR/J/AJ/98/1305
- Title:
- Stellar content of NGC 346
- Short Name:
- J/AJ/98/1305
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using CCD UBV photometry and spectroscopy, we have investigated the stellar content of NGC 346, the brightest H II region in the SMC. Spectra of 42 stars confirm that 33 are of O type, of which 11 are of type O6.5 or earlier; this is as many early-type O stars as is known in the rest of the SMC. From the spectroscopy and photometry we are able to construct an H-R diagram which is essentially complete down to ~10M_{sun}_. We find an initial mass-function slope {GAMMA}=-1.9, similar to that found for massive stars near the Sun and in the LMC: the presence of six stars in the mass range 40-85M_{sun}_ suggests that the upper-mass limit of the IMF is also not appreciably lower in the SMC than it is in the Galaxy. Our photometry has identified five probable red supergiants of which one was previously known. These stars, plus two B supergiants, are evolved stars of considerably lower mass (15M_{sun}_) than many of the unevolved cluster members. Most of these lower-mass, evolved stars form a spatially distinct subgroup; we believe that NGC 346 thus provides an example of sequential star formation in the SMC. We also have identified a background field population of 5M_{sun}_ stars. We find that the ionizing flux from the hot stars is consistent with the previously known Half nebular luminosity. Finally, we discuss the enigmatic W-R binary HD 5980, which our point-spread-function fitting has identified as a close visual double.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/139
- Title:
- Three O-type binaries photometry in LMC
- Short Name:
- J/ApJ/789/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper in a series devoted to the study of massive binary systems in the Large Magellanic Cloud (LMC). We mainly aim to provide accurate data that constrains the mass-luminosity relation for the most massive stars but also to address the long lasting problem known as the "mass discrepancy." We present here our results for three binaries (LMC 169782, LMC 171520, and [P93] 921) harboring the earliest O-type components-ranging from O4 V to O6.5 V-among our sample of 17 systems. Our photometry provided accurate periods for the studied systems, allowing the spectroscopic observations to be performed at selected phases where the radial velocity separation between binary components is larger. Following the procedure outlined in our first paper of this series, after solving the radial velocity curves for orbital parameters, we used tomographic reconstruction to obtain the individual spectra of each star, from which we determined effective temperatures via a model atmosphere fitting with FASTWIND. This information, combined with the light-curve analysis that was performed with GENSYN, enabled the determination of absolute masses, radii, and bolometric luminosities that are compared with those predicted by modern stellar evolutionary models finding that they agree within the uncertainties. Nevertheless, the comparison seems to confirm the small differences found in the first paper of this series in the sense that the evolutionary masses are slightly larger than the Keplerian ones, with differences averaging ~10%, or alternatively, the stellar evolutionary models predict luminosities that are somewhat lower than observed. Still, the overall agreement between the current evolutionary models and the empirically determined stellar parameters is remarkable.
- ID:
- ivo://CDS.VizieR/J/A+A/457/637
- Title:
- UBVJHK synthetic photometry of Galactic O stars
- Short Name:
- J/A+A/457/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The development of powerful infrared observational techniques enables the study of very extincted objects and young embedded star-forming regions. This is especially interesting in the context of massive stars that form and spend a non negligible fraction of their life still enshrouded in their parental molecular cloud. Spectrophotometric calibrations are thus necessary to constrain the physical properties of heavily extincted objects.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A40
- Title:
- VFTS. O-type stellar content of 30 Dor
- Short Name:
- J/A+A/564/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed spectral classifications are presented for 352 O-B0 stars in the VLT-FLAMES Tarantula Survey ESO Large Programme, of which 213 O-type are judged of sufficiently high quality for further morphological analysis. Among them, six subcategories of special interest are distinguished. (1) Several new examples of the earliest spectral types O2-O3 have been found, while a previously known example has been determined to belong to the nitrogen-rich ON2 class. (2) A group of extremely rapidly rotating main-sequence objects has been isolated, including the largest vsini values known, the spatial and radial-velocity distributions of which suggest ejection from the two principal ionizing clusters NGC 2070 and NGC 2060. (3) Several new examples of the evolved, rapidly rotating Onfp class show similar evidence, although at least some of them are spectroscopic binaries. (4) No fewer than 48 members of the Vz category, hypothesized to be on or near the zero-age main sequence, are found in this sample; in contrast to the rapid rotators, they are strongly concentrated to the ionizing clusters and a newly recognized region of current and recent star formation to the north, supporting their interpretation as very young objects, as do their relatively faint absolute magnitudes. (5) A surprisingly large fraction of the main-sequence spectra belong to the recently recognized V((fc)) class, with CIII emission lines of similar strength to the usual NIII in V((f)) spectra, although a comparable number of the latter are also present, as well as six objects with very high-quality data but no trace of either emission feature, presenting new challenges to physical interpretations. (6) Two mid-O Vz and three late-O giant/supergiant spectra with morphologically enhanced nitrogen lines have been detected. Absolute visual magnitudes have been derived for each star with individual extinction laws, and composite Hertzsprung-Russell diagrams provide evidence of the multiple generations present in this field. Spectroscopic binaries, resolved visual multiples, and possible associations with X-ray sources are noted. Astrophysical and dynamical analyses of this unique dataset underway will provide new insights into the evolution of massive stars and starburst clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/380/258
- Title:
- V light curve of AzV 73
- Short Name:
- J/A+A/380/258
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A CCD V light curve for the eclipsing binary star AzV 73 is presented. This new photometric observations are analysed together with previously published CCD I photometry from Udalski et al. (1998AcA....48..563U) and spectrographic data from Niemela & Bassino (1994ApJ...437..332N), by means of the Wilson-Devinney code. It is found that this system is semi-detached, with an orbital inclination of roughly 86{deg} and a separation of 42R_{sun}_. The sizes and masses are R_1_=11.53 +/-0.5R_{sun}_, M_1_=25.26+/-0.7M_{sun}_, and R_2_=15.46+/-0.4R_{sun}_, M_2_=21.96+/-0.8M_{sun}_ for the primary and secondary components, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A81
- Title:
- VLTS. 30Dor O giants and supergiants
- Short Name:
- J/A+A/600/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Tarantula region in the Large Magellanic Cloud contains the richest population of spatially resolved massive O-type stars known so far. This unmatched sample offers an opportunity to test models describing their main-sequence evolution and mass-loss properties. Using ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to determine stellar, photospheric and wind properties of 72 presumably single O-type giants, bright giants and supergiants and to confront them with predictions of stellar evolution and of line-driven mass-loss theories. We apply an automated method for quantitative spectroscopic analysis of O stars combining the non-LTE stellar atmosphere model FASTWIND with the genetic fitting algorithm PIKAIA to determine the following stellar properties: effective temperature, surface gravity, mass-loss rate, helium abundance, and projected rotational velocity. The latter has been constrained without taking into account the contribution from macro-turbulent motions to the line broadening. We present empirical effective temperature versus spectral subtype calibrations at LMC-metallicity for giants and supergiants. The calibration for giants shows a +1kK offset compared to similar Galactic calibrations; a shift of the same magnitude has been reported for dwarfs. The supergiant calibrations, though only based on a handful of stars, do not seem to indicate such an offset. The presence of a strong upturn at spectral type O3 and earlier can also not be confirmed by our data. In the spectroscopic and classical Hertzsprung-Russell diagrams, our sample O stars are found to occupy the region predicted to be the core hydrogen-burning phase by state-of-the-art models. For stars initially more massive than approximately 60M_{sun}_ the giant phase already appears relatively early on in the evolution; the supergiant phase develops later. Bright giants, however, are not systematically positioned between giants and supergiants at M_init_>25M_{sun}. At masses below 60M_{sun} the dwarf phase clearly precedes the giant and supergiant phases; however this behavior seems to break down at $M_init_<18M_{sun}_. Here, stars classified as late O III and II stars occupy the region where O9.5-9.7V stars are expected, but where few such late O V stars are actually seen. Though we can not exclude that these stars represent a physically distinct group, this behaviour may reflect an intricacy in the luminosity classification at late O spectral subtype. Indeed, on the basis of a secondary classification criterion, the relative strength of SiIV to HeI absorption lines, these stars would have been assigned a luminosity class IV or V. Except for five stars, the helium abundance of our sample stars is in agreement with the initial LMC composition. This outcome is independent of their projected spin rates. The aforementioned five stars present moderate projected rotational velocities (i.e., vrot<200km/s) and hence do not agree with current predictions of rotational mixing in main-sequence stars. They may potentially reveal other physics not included in the models such as binary-interaction effects. Adopting theoretical results for the wind velocity law, we find modified wind momenta for LMC stars that are ~0.3dex higher than earlier results. For stars brighter than 10^5^L_[sun}_, that is, in the regime of strong stellar winds, the measured (unclumped) mass-loss rates could be considered to be in agreement with line-driven wind predictions if the clump volume filling factors were f_V_~1/8 to 1/6.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A82
- Title:
- VLTS. O giants and supergiants nitrogen abundances
- Short Name:
- J/A+A/600/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretically, rotation-induced chemical mixing in massive stars has far reaching evolutionary consequences, affecting the sequence of morphological phases, lifetimes, nucleosynthesis, and supernova characteristics. Using a sample of 72 presumably single O-type giants to supergiants observed in the context of the VLT-FLAMES Tarantula Survey (VFTS), we aim to investigate rotational mixing in evolved core-hydrogen burning stars initially more massive than 15M_{sun}_ by analysing their surface nitrogen abundances. Using stellar and wind properties derived in a previous VFTS study we computed synthetic spectra for a set of up to 21 N II-V lines in the optical spectral range, using the non-LTE atmosphere code FASTWIND. We constrained the nitrogen abundance by fitting the equivalent widths of relatively strong lines that are sensitive to changes in the abundance of this element. Given the quality of the data, we constrained the nitrogen abundance in 38 cases; for 34 stars only upper limits could be derived, which includes almost all stars rotating at vrot>200km/s. We analysed the nitrogen abundance as a function of projected rotation rate vrot and confronted it with predictions of rotational mixing. We found a group of N-enhanced slowly-spinning stars that is not in accordance with predictions of rotational mixing in single stars. Among O-type stars with (rotation-corrected) gravities less than logg_c_=3.75 this group constitutes 30-40 percent of the population. We found a correlation between nitrogen and helium abundance which is consistent with expectations, suggesting that, whatever the mechanism that brings N to the surface, it displays CNO-processed material. For the rapidly-spinning O-type stars we can only provide upper limits on the nitrogen abundance, which are not in violation with theoretical expectations. Hence, the data cannot be used to test the physics of rotation induced mixing in the regime of high spin rates. While the surface abundances of 60-70 percent of presumed single O-type giants to supergiants behave in conformity with expectations, at least 30-40 percent of our sample can not be understood in the current framework of rotational mixing for single stars. Even though we have excluded stars showing radial velocity variations, of our sample may have remained contaminated by post-interaction binary products. Hence, it is plausible that effects of binary interaction need to be considered to understand their surface properties. Alternatively, or in conjunction, the effects of magnetic fields or alternative mass-loss recipes may need to be invoked.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A79
- Title:
- VLTS. Properties of O dwarf in 30 Dor
- Short Name:
- J/A+A/601/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VLT-FLAMES Tarantula Survey has observed hundreds of O-type stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). We study the properties of 105 apparently single O-type dwarfs. To determine stellar and wind parameters, we used the IACOB-GBAT package, an automatic procedure based on a large grid of atmospheric models calculated with the FASTWIND code. In addition to classical techniques, we applied the Bayesian BONNSAI tool to estimate evolutionary masses. We provide a new calibration of effective temperature vs. spectral type for O-type dwarfs in the LMC, based on our homogeneous analysis of the largest sample of such objects to date and including all spectral subtypes. Good agreement with previous results is found, although the sampling at the earliest subtypes could be improved. Rotation rates and helium abundances are studied in an evolutionary context. We find that most of the rapid rotators (vsini higher than 300km/s) in our sample have masses below 25 MSun and intermediate rotation-corrected gravities (logg_c_ between 3.9 and 4.1). Such rapid rotators are scarce at higher gravities (i.e. younger ages) and absent at lower gravities (larger ages). This is not expected from theoretical evolutionary models, and does not appear to be due to a selection bias in our sample. We compare the estimated evolutionary and spectroscopic masses, finding a trend that the former is higher for masses below 20M_{sun}_. This can be explained as a consequence of limiting our sample to the O-type stars, and we see no compelling evidence for a systematic mass discrepancy. For most of the stars in the sample we were unable to estimate the wind-strength parameter (hence mass-loss rates) reliably, particularly for objects with luminosity lower than logL/L_{sun}_ about 5.1. Ultraviolet spectroscopy is needed to undertake a detailed investigation of the wind properties of these dwarfs.
