- ID:
- ivo://CDS.VizieR/J/A+A/304/415
- Title:
- uvby-Hbeta photometry of Eta Car 1992-94
- Short Name:
- J/A+A/304/415
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyze two seasons of intense photometric monitoring in the Stroemgren uvbyH{beta} system of {eta} Carinae (October 1992-August 1994). The luminous blue variable (LBV) in the core did not show much S Dor activity, i.e. it was in a relatively quiescent stage. This situation was very favourable for studying its optical micro variations. It appears that the central LBV pulsates (presumably in a non-radial mode) like other massive evolved stars, the {alpha} Cyg variables. The quasi-period is 58.56d. The linear ephemeris is: JD_max_=2448875.0 +58.56 E. Support was found for the existence of the presumed periodicity of 52.4d of the so-called "dimples", shallow dips in the light curve which only last for a few days. The cause may be the eclipse of a small companion or of a hot spot in an accretion disk. The H{beta} index became bluer by ~0.07mag during the last 11/2 years and shows an oscillation in anti-phase with the 58.56d pulsation, suggesting that the HII region(s) responsible for the hydrogen line emission has a relatively high luminosity. This is another reason to suppose that a second luminous source, perhaps a luminous disk (with a hot spot), may be present in the {eta} Car system.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/PAZh/36/281
- Title:
- Variability of 3 protoplanetary nebulae
- Short Name:
- J/PAZh/36/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new photometric data and analyze long-term UBV observations of three candidates for protoplanetary nebulae - F supergiants with infrared excesses at high Galactic latitudes -IRAS 18095+2704, IRAS 19386+0155, and IRAS 19500-1709. All these stars exhibit quasi-periodic low-amplitude variations caused by pulsations against the background of long-term brightness trends. For IRAS 18095+2704 = V887 Her, we have found a pulsation period of 109 days and revealed a linear brightness trend - the star brightens at constant (within the limits of the measurement errors) yearly mean color indices. The light curve of IRAS 19386+0155 = V1648 Aql in 2000-008 is represented by a wave with a fundamental period of 102 days whose modulation with a close period of 98 days leads to variations with a variable amplitude. V1648 Aql also shows a systematic rise in V brightness along with a reddening. IRAS 19500-1709 = V5112 Sgr exhibits irregular pulsations with periods of 39 and 47 days. The long-term variability component of V5112 Sgr may indicate that the star is binary.
- ID:
- ivo://CDS.VizieR/J/A+A/337/779
- Title:
- V810 Cen Geneva photometry
- Short Name:
- J/A+A/337/779
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The light curve of the yellow supergiant V810 Centauri in the Geneva photometric system has been analysed with Date Compensate Fourier Transform and Weighted Wavelet Z-transform. Two periods around 150 and 100 days dominate the frequency spectrum but variable amplitudes and other modes are required to fully reproduce whole data set.
- ID:
- ivo://CDS.VizieR/J/PAZh/42/831
- Title:
- V1027 Cygni UBV and JHKLM photometry
- Short Name:
- J/PAZh/42/831
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our UBV and JHKLM photometry for the semiregular pulsating variable V1027 Cyg, a supergiant with an infrared excess, over the period from 1997 to 2015 (UBV) and in 2009-2015 (JHKLM). Together with the new data, we analyze the photometric observations of V1027 Cyg that we have obtained and published previously. Our search for a periodicity in the UBV brightness variations has led to several periods from P=212d to 320d in different time intervals. We have found the period P=237d based on our infrared photometry. The variability amplitude, the lightcurve shape, and the magnitude of V1027 Cyg at maximum light change noticeably from cycle to cycle.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A70
- Title:
- VLT-FLAMES Tarantula Survey: B supergiants
- Short Name:
- J/A+A/575/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Model atmosphere analyses have been previously undertaken for both Galactic and extragalactic B-type supergiants. By contrast, little attention has been given to a comparison of the properties of single supergiants and those that are members of multiple systems. Atmospheric parameters and nitrogen abundances have been estimated for all the B-type supergiants identified in the VLT-FLAMES Tarantula survey. These include both single targets and binary candidates. The results have been analysed to investigate the role of binarity in the evolutionary history of supergiants. TLUSTY non-local thermodynamic equilibrium (LTE) model atmosphere calculations have been used to determine atmospheric parameters and nitrogen abundances for 34 single and 18 binary supergiants. Effective temperatures were deduced using the silicon balance technique, complemented by the helium ionisation in the hotter spectra. Surface gravities were estimated using Balmer line profiles and microturbulent velocities deduced using the silicon spectrum. Nitrogen abundances or upper limits were estimated from the NII spectrum. The effects of a flux contribution from an unseen secondary were considered for the binary sample. We present the first systematic study of the incidence of binarity for a sample of B-type supergiants across the theoretical terminal age main sequence (TAMS).
- ID:
- ivo://CDS.VizieR/J/A+A/614/A12
- Title:
- VLTI/PIONIER observations of CE Tauri
- Short Name:
- J/A+A/614/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red supergiant stars represent one of the latest stages of the evolution of massive stars. Their photospheric convection may play an important role in the launching mechanism of their mass loss. Yet, its characteristics and dynamics are poorly constrained. By observing red supergiant stars with near infrared interferometry at different epochs, we expect to unveil the evolution of bright convective features on their stellar surface. We observed the M2Iab-Ib red supergiant star CE Tau with the VLTI/PIONIER instrument in the H band at two different epochs separated by one month. We derive the angular diameter of the star, basic stellar parameters and reconstruct two reliable images of its H band photosphere. The contrast of the convective pattern of the reconstructed images is 5+/-1% and 6+/-1 % for our two epochs of observation. The stellar photosphere shows few changes between the two epochs. The contrast of the convective pattern is below the average contrast variations obtained on 30 randomly chosen snapshots of the best matching 3D radiative hydrodynamics simulation: 23+/-1% for the original simulation images, and 16+/-1% for the maps degraded to the reconstruction resolution. We offer two hypotheses to explain this observation: CE Tau may be experiencing a quiet convective activity episode or it could be a consequence of its warmer effective temperature (hence its smaller radius) compared to the simulation.
- 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/AJ/153/115
- Title:
- VLT/SINFONI observations of MIPSGAL "bubbles"
- Short Name:
- J/AJ/153/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared H- and K-band spectra of potential central stars within the inner 8"-by-8" regions of 55 MIPSGAL "bubbles" (MBs), sub-arcminute circumstellar shells discovered in the mid-IR survey of the Galactic plane with Spitzer/MIPS. At magnitudes brighter than 15, we detect a total of 230 stars in the K band and 179 stars in the H band. We spectrally identify 145 stars in all but three MBs, with average magnitudes of 13.8 and 12.7 respectively, using spectral libraries and previous studies of near-IR stellar spectra. We also use tabulated intrinsic stellar magnitudes and colors to derive distances and extinction values, and to better constrain the classifications of the stars. We reliably identify the central sources for 21 of the 55 MBs, which we classify as follows: one Wolf-Rayet, three luminous blue variable candidates, four early-type (O to F), and 15 late-type (G to M) stars. The 21 central sources are, on average, one magnitude fainter than these in the most recent study of MBs, and we notice a significant drop in the fraction of massive star candidates. For the 34 remaining MBs in our sample, we are unable to identify the central sources due to confusion, low spectroscopic signal-to-noise ratio, and/or lack of detections in the images near the centers of the bubbles. We discuss how our findings compare with previous studies and support the trend, for the most part, between the shells' morphologies in the mid-IR and central sources spectral types.
- ID:
- ivo://CDS.VizieR/J/ApJ/501/153
- Title:
- VRB photometry of red supergiants
- Short Name:
- J/ApJ/501/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the red supergiant (RSG) population of nearby galaxies allows us to probe massive star evolution as a function of metallicity; however, contamination by foreground Galactic dwarfs dominates surveys for red stars in Local Group galaxies beyond the Magellanic Clouds. Model atmospheres predict that low-gravity supergiants will have B-V values that are redder by several tenths of a magnitude than foreground dwarfs at a given V-R color, a result that is largely independent of reddening. We conduct a BVR survey of several fields in the Local Group galaxies NGC 6822, M33, and M31 as well as neighboring control fields and identify RSG candidates from CCD photometry. The survey is complete to V=20.5, corresponding to M_V_=-4.5 or an M_bol_ of -6.3 for the reddest stars. Follow-up spectroscopy at the Ca II triplet of 130 stars is used to demonstrate that our photometric criterion for identifying RSGs is highly successful (96% for stars brighter than V=19.5; 82% for V=19.5-20.5). Classification spectra are also obtained for a number of stars in order to calibrate color with spectral type empirically.
- ID:
- ivo://CDS.VizieR/J/PAZh/37/691
- Title:
- V340 Ser and V448 Lac light curves
- Short Name:
- J/PAZh/37/691
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze long-term UBV observations and ASAS-3 photometry for five candidates for protoplanetary nebulae - F and G supergiants with infrared excesses at high Galactic latitudes - V340 Ser, IRAS 05113+1347, V552 Pup, V448 Lac, and RV Col. These stars exhibit quasi-periodic multifrequency light variations caused by pulsations with characteristic time scales from 83 to 139 days, depending on the stellar temperature. Cooler stars undergo variations with larger amplitudes and periods. The variations at close frequencies with a period ratio of 1.03-1.09 are responsible for the amplitude modulation revealed for most program stars.
