- 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/AJ/150/190
- Title:
- Spectroscopy and Stromgren photometry of HR 1040
- Short Name:
- J/AJ/150/190
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A time-series analysis of spectroscopic and photometric observables of the A0 Ia supergiant HR 1040 has been performed, including equivalent widths, radial velocities, and Stromgren photometric indices. The data, obtained from 1993 through 2007, include 152 spectroscopic observations from the Ritter Observatory 1m telescope and 269 Stromgren photometric observations from the Four College Automated Photoelectric Telescope. Typical of late B- and early A-type supergiants, HR 1040 has a highly variable H{alpha} profile. The star was found to have an intermittent active phase marked by correlation between the H{alpha} absorption equivalent width and blue-edge radial velocity and by photospheric connections observed in correlations to equivalent width, second moment and radial velocity in SiII{lambda}{lambda}6347,6371. High-velocity absorption (HVA) events were observed only during this active phase. HVA events in the wind were preceded by photospheric activity, including SiII radial velocity oscillations 19-42 days prior to onset of an HVA event and correlated increases in SiII W_{lambda}_ and second moment from 13 to 23 days before the start of the HVA event. While increases in various line equivalent widths in the wind prior to HVA events have been reported in the past in other stars, our finding of precursors in enhanced radial velocity variations in the wind and at the photosphere is a new result.
- ID:
- ivo://CDS.VizieR/J/A+AS/129/541
- Title:
- Spectroscopy of IRC +10420
- Short Name:
- J/A+AS/129/541
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A high resolution optical spectrum of the post-red supergiant candidate IRC +10420 is presented. The Utrecht Echelle Spectrograph observations, with a total integration time of more than 9 hours provide a spectral coverage from 3850 A to 1micron, and a spectral resolution of 9km/s. The spectrum is shown, and an identification list of lines in the spectrum is provided. From a preliminary analysis of the spectrum we find that the spectral type of IRC+10420 has changed from F8I+ in 1973 to mid- to early A type now, confirming the results of Oudmaijer et al. (1996MNRAS.280.1062O), who claimed a change in temperature based on photometric changes. It is shown that most of the emission lines in the spectrum of IRC +10420 are blue-shifted with respect to the systemic velocity traced by circumstellar rotational CO emission, while the (few) absorption lines - with the exception of some high excitation lines - are red-shifted by 25km/s, which may suggest infall of material onto the star. Finally, it is found that the interstellar extinction towards IRC +10420, as traced by the Diffuse Interstellar Bands is very large, with an inferred E(B-V) of 1.4+/-0.5 compared to a total E(B-V) of 2.4. This table provides the line identifications for the measured spectral lines from atomic species. Listed in the table are respectively the laboratory wavelength (in air) taken from Moore (1945, in A multiplet table of astrophysical interest, Contribution from the Princeton University Observatory No. 20.), the line identification (ion and multiplet), the energies of the lower levels of the transitions in eV, and the log(gf). The latter two values are taken from Wiese et al. (1966, Nat. Stand. Ref. Data Ser. 20 and 1969, Nat. Stand. Ref. Data Ser. 22), Martin et al. (1988, Cat. <VI/72>) and Fuhr et al. (1988, Cat. <VI/72>). The spectral lines that are marked `UN' were not identified, the wavelength given for these lines is the observed wavelength. Then next entries in the table are the velocity shift of the centres of spectral lines (in LSR), the equivalent width in milli-Angstrom, and the full-width-at-half maximum of the fit in Angstrom. The velocity shifts have been measured by fitting Gaussian profiles through the lines, the equivalent widths have been measured by integrating the line over the continuum. In the case of overlapping lines, the lines were de-composed by fitting multiple Gaussian components to the profiles. In these cases (marked with `deb.' in the table) the equivalent widths are the areas under the Gaussian fits. Equivalent widths for lines that could not be deblended, are given between brackets. These values represent the total equivalent width of the lines concerned.
- ID:
- ivo://CDS.VizieR/J/A+AS/96/269
- Title:
- Stellar Models from 0.8 to 120 Msolar
- Short Name:
- J/A+AS/96/269
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New grids of stellar evolutionary models covering the range of 0.8 to 120 solar masses have been computed for metallicites Z=0.020 and Z=0.001. The models use the new opacities by Rogers and Iglesias (1992ApJS...79..507R) and by Kurucz (1991) at low T. The consequent changes in the solar helium content, in the mixing length ratio and in the overshooting parameter are taken into account after careful calibrations. Important physical ingredients as the nuclear reaction rates and the neutrino loss rates have been updated. The ionization of the main heavy elements is calculated in details. Results of the models are given in a compact way at corresponding evolutionary stages in each model. In addition to the tables, we shortly present some general results on the tracks in the HR diagrams, the lifetimes in the H-, He-, C-burning phases, and on massive and WR stars.
- ID:
- ivo://CDS.VizieR/J/A+A/558/A103
- Title:
- Stellar models with rotation. 0.8<M<120, Z=0.002
- Short Name:
- J/A+A/558/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the impact of a subsolar metallicity on various properties of non-rotating and rotating stars, such as surface velocities and abundances, lifetimes, evolutionary tracks, and evolutionary scenarios. We provide a grid of single star models covering a mass range of 0.8 to 120M_{sun_} with an initial metallicity Z=0.002 with and without rotation. We discuss the impact of a change in the metallicity by comparing the current tracks with models computed with exactly the same physical ingredients but with a metallicity Z=0.014 (solar). We show that the width of the main-sequence (MS) band in the upper part of the Hertzsprung-Russell diagram (HRD), for luminosity above log(L/L_{sun}_)>5.5, is very sensitive to rotational mixing. Strong mixing significantly reduces the MS width. Here for the first time over the whole mass range, we confirm that surface enrichments are stronger at low metallicity provided that comparisons are made for equivalent initial mass, rotation, and evolutionary stage. We show that the enhancement factor due to a lowering of the metallicity (all other factors kept constant) increases when the initial mass decreases. Present models predict an upper luminosity for the red supergiants (RSG) of log (L/L_{sun}_) around 5.5 at Z=0.002 in agreement with the observed upper limit of RSG in the Small Magellanic Cloud. We show that models using shear diffusion coefficient, which is calibrated to reproduce the surface enrichments observed for MS B-type stars at Z=0.014, can also reproduce the stronger enrichments observed at low metallicity. In the framework of the present models, we discuss the factors governing the timescale of the first crossing of the Hertzsprung gap after the MS phase. We show that any process favouring a deep localisation of the H-burning shell (steep gradient at the border of the H-burning convective core, low CNO content), and/or the low opacity of the H-rich envelope favour a blue position in the HRD for the whole, or at least a significant fraction, of the core He-burning phase.
- ID:
- ivo://CDS.VizieR/J/A+A/537/A146
- Title:
- Stellar models with rotation. 0.8<M<120, Z=0.014
- Short Name:
- J/A+A/537/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many topical astrophysical research areas, such as the properties of planet host stars, the nature of the progenitors of different types of supernovae and gamma ray bursts, and the evolution of galaxies, require complete and homogeneous sets of stellar models at different metallicities in order to be studied during the whole of cosmic history. We present here a first set of models for solar metallicity, where the effects of rotation are accounted for in a homogeneous way. We computed a grid of 48 different stellar evolutionary tracks, both rotating and non-rotating, at Z=0.014, spanning a wide mass range from 0.8 to 120M_{sun}_. For each of the stellar masses considered, electronic tables provide data for 400 stages along the evolutionary track and at each stage, a set of 43 physical data are given. These grids thus provide an extensive and detailed data basis for comparisons with the observations. The rotating models start on the ZAMS with a rotation rate v_ini_/v_crit_=0.4. The evolution is computed until the end of the central carbon-burning phase, the early AGB phase, or the core helium-flash for, respectively, the massive, intermediate, and both low and very low mass stars. The initial abundances are those deduced by Asplund et collaborators, which best fit the observed abundances of massive stars in the solar neighbourhood. We update both the opacities and nuclear reaction rates, and introduce new prescriptions for the mass-loss rates as stars approach the Eddington and/or the critical velocity. We account for both atomic diffusion and magnetic braking in our low-mass star models. The present rotating models provide a good description of the average evolution of non-interacting stars. In particular, they reproduce the observed MS width, the positions of the red giant and supergiant stars in the HR diagram, the observed surface compositions and rotational velocities. Very interestingly, the enhancement of the mass loss during the RSG stage, when the luminosity becomes supra-Eddington in some outer layers, help models above 15-20 Msun to lose a significant part of their hydrogen envelope and evolve back into the blue part of the HR diagram. This result has interesting consequences for the blue to red supergiant ratio, the minimum mass for stars to become WR stars, and the maximum initial mass of stars that explode as type II-P supernovae.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A99
- Title:
- 2 supergiants and 2 hypergiants radio spectra
- Short Name:
- J/A+A/545/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Herschel/HIFI spectra observed towards two Red Supergiants (NML Cyg, Betelgeuse) and two Yellow Hypergiants (AFGL2343, IRC+10420). The data focus on various transitions of ^12^CO, ^13^CO, ortho- and para- water, as well as some other bonus lines such as SiO, OH or NH_3_.
- ID:
- ivo://CDS.VizieR/J/AJ/112/2559
- Title:
- Supergiants in NGC 672
- Short Name:
- J/AJ/112/2559
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- V, R, and I CCD images are used to investigate the photometric properties and spatial distribution of supergiants in the nearby interacting galaxy NGC 672. Not counting stars imbedded in H II regions, our sample consists of 237 objects. The (V-R,V-I) two-color diagram indicates that the majority of these stars have spectral types between A-K. Statistical tests show that the outer region of NGC 672 contains a redder population of supergiants than the inner region. Comparisons with theoretical evolutionary tracks indicate that the majority of the supergiants in NGC 672 have progenitor masses between 15M_{sun}_ and 25M_{sun}_, and that the inner regions contain stars that are more massive than in the outer disk, indicating that an age gradient is present. The luminosity functions in all three bandpasses follow power laws, and the exponent in V=0.79+/-0.06, in good agreement with other galaxies. The brightest red supergiants occur at V~22.0, from which we derive a distance modulus of 29.5, corresponding to 7.9(+1.0)(-0.9)Mpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/687/230
- Title:
- Survey of M31 with Spitzer
- Short Name:
- J/ApJ/687/230
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the stellar population of M31 in a Spitzer Space Telescope survey utilizing IRAC and MIPS observations. Red supergiants are the brightest objects seen in the infrared; they are a prominent evolutionary phase. Due to their circumstellar envelopes, many of these radiate the bulk of their luminosity at IRAC wavelengths and do not stand out in the near-infrared or optically. Going fainter, we see large numbers of luminous asymptotic giant branch stars (AGB), many of which are known long-period variables. Relative to M33 the AGB carbon star population of M31 appears sparse, but this needs to be spectroscopically confirmed.
- ID:
- ivo://CDS.VizieR/VI/125
- Title:
- Theoretical spectra of red giants and supergiants
- Short Name:
- VI/125
- Date:
- 10 Mar 2022
- Publisher:
- CDS
- Description:
- It remains difficult to interpret the near-IR emission of young stellar populations. One main reason is our incomplete understanding of the spectra of luminous red stars. This work provides a grid of theoretical spectra of red giant (RG) and red supergiant (RSG) stars, that extends through optical and near-IR wavelengths. For the first time, models are also provided with modified surface abundances of C, N and O, as a step towards accounting for the changes that occur due to convective dredge-up in red supergiants or may occur at earlier evolutionary stages in the case of rotation. The aims are (i) to assess how well current models reproduce observed spectra, in particular in the near-IR; (ii) to quantify the effects of the abundance changes on the spectra; and (iii) to determine how these changes affect estimates of fundamental stellar parameters.
