Topic
Deneb
About: Deneb is a research topic. Over the lifetime, 36 publications have been published within this topic receiving 422 citations. The topic is also known as: Alpha Cygni & A Cygni.
Papers
TL;DR: In this paper, the spectral properties of luminous BA-type supergiants were derived from high-S/N and high-resolution spectra in the visual and near-IR.
Abstract: Context. Quantitative spectroscopy of luminous BA-type supergiants offers a high potential for modern astrophysics. Detailed studies allow the evolution of massive stars, galactochemical evolution, and the cosmic distance scale to be constrained observationally. Aims. A detailed and comprehensive understanding of the atmospheres of BA-type supergiants is required in order to use this potential properly. The degree to which we can rely on quantitative studies of this class of stars as a whole depends on the quality of the analyses for benchmark objects. We constrain the basic atmospheric parameters and fundamental stellar parameters, as well as chemical abundances of the prototype A-type supergiant Deneb to unprecedented accuracy by applying a sophisticated analysis methodology, which has recently been developed and tested. Methods. The analysis is based on high-S/N and high-resolution spectra in the visual and near-IR. Stellar parameters and abundances for numerous astrophysically interesting elements are derived from synthesis of the photospheric spectrum using a hybrid non-LTE technique, i.e. line-blanketed LTE model atmospheres and non-LTE line formation. Multiple metal ionisation equilibria and numerous hydrogen lines from the Balmer, Paschen, Brackett, and Pfund series are utilised simultaneously for the stellar parameter determination. The stellar wind properties are derived from Ha line-profile fitting using line-blanketed hydrodynamic non-LTE models. Further constraints come from matching the photospheric spectral energy distribution from the UV to the near-IR L band. Results. The atmospheric parameters of Deneb are tightly constrained: effective temperature T eff = 8525 ± 75 K, surface gravity logg = 1.10±0.05, microturbulence ξ = 8±1 km s -1 , macroturbulence, and projected rotational velocity v sin i are both 20±2 km s -1 . The abundance analysis gives helium enrichment by 0.10 dex relative to solar and an N/C ratio of 4.44 ± 0.84 (mass fraction), implying strong mixing with CN-processed matter. The heavier elements are consistently underabundant by ∼0.20 dex compared to solar. Peculiar abundance patterns, which were suggested in previous analyses cannot be confirmed. Accounting for non-LTE effects is essential for removing systematic trends in the abundance determination, for minimising statistical 1σ-uncertainties to ≤10-20% and for establishing all ionisation equilibria at the same time. Conclusions. A luminosity of (1.96±0.32)±10 5 L ⊙ , a radius of 203 ± 17 R ⊙ , and a current mass of 19±4 M ⊙ are derived. Comparison with stellar evolution predictions suggests that Deneb started as a fast-rotating late O-type star with M ZAMS ≃ 23 M ⊙ on the main sequence and is currently evolving to the red supergiant stage.
69 citations
TL;DR: In this article, the basic atmospheric parameters and fundamental stellar parameters as well as chemical abundances of the prototype A-type supergiant Deneb were derived by applying a sophisticated hybrid NLTE spectrum synthesis technique.
Abstract: Quantitative spectroscopy of luminous BA-type supergiants offers a high potential for modern astrophysics. The degree to which we can rely on quantitative studies of this class of stars as a whole depends on the quality of the analyses for benchmark objects. We constrain the basic atmospheric parameters and fundamental stellar parameters as well as chemical abundances of the prototype A-type supergiant Deneb to unprecedented accuracy (Teff = 8525 +/- 75 K, log(g) = 1.10 +/- 0.05 dex, M_spec = 19 +/- 3 M_sun, L = 1.96 +/- 0.32 *10^5 L_sun, R = 203 +/- 17 R_sun, enrichment with CN-processed matter) by applying a sophisticated hybrid NLTE spectrum synthesis technique which has recently been developed and tested. The study is based on a high-resolution and high-S/N spectrum obtained with the Echelle spectrograph FOCES on the Calar Alto 2.2m telescope. Practically all inconsistencies reported in earlier studies are resolved. Multiple metal ionization equilibria and numerous hydrogen lines from the Balmer, Paschen, Brackett and Pfund series are brought into match simultaneously for the stellar parameter determination. Stellar wind properties are derived from H_alpha line-profile fitting using line-blanketed hydrodynamic non-LTE models. A self-consistent view of Deneb is thus obtained, allowing us to discuss its evolutionary state in detail by comparison with the most recent generation of evolution models for massive stars. (abridged)
39 citations
TL;DR: A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds as mentioned in this paper.
Abstract: A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of mm and cm emission (obtained using the SCUBA and the VLA), as well a strong upper limit on the 850 micron flux (using the HHT). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement, 2.40 +/- 0.06 mas, from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600 +/- 500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 A to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of 8400 +/- 100 K and 8 +/- 3 E-7 M_sun/yr, respectively. This range of mass-loss rates is consistent with that derived from high dispersion UV spectra when non-LTE metal-line blanketing is considered. We are unable achieve a reasonable fit to a typical Halpha P-Cygni profile with any model parameters over a reasonable range. This is troubling because the \ha profile is the observational basis for Wind Momentum-Luminosity Relationship.
35 citations
TL;DR: In this paper, the authors employ optical interferometry to study the Halpha line-formation region in these stellar environments, and assess the impact of the wind on the visible and near-IR interferometric signatures, using both Balmer-line and continuum photons.
Abstract: BA-type supergiants are amongst the most optically-bright stars. They are observable in extragalactic environments, hence potential accurate distance indicators. Emission activity in the Halpha line of the BA supergiants Rigel (B8Ia) and Deneb (A2Ia) is indicative of presence of localized time-dependent mass ejections. Here, we employ optical interferometry to study the Halpha line-formation region in these stellar environments. High spatial- (0.001 arcsec) and spectral- (R=30 000) resolution observations of Halpha were obtained with the visible recombiner VEGA installed on the CHARA interferometer, using the S1S2 array-baseline (34m). Six independent observations were done on Deneb over the years 2008 and 2009, and two on Rigel in 2009. We analyze this dataset with the 1D non-LTE radiative-transfer code CMFGEN, and assess the impact of the wind on the visible and near-IR interferometric signatures, using both Balmer-line and continuum photons. We observe a visibility decrease in Halpha for both Rigel and Deneb, suggesting that the line-formation region is extended (1.5-1.75 R*). We observe a significant visibility decrease for Deneb in the SiII6371 line. We witness time variations in the differential phase for Deneb, implying an inhomogeneous and unsteady circumstellar environment, while no such variability is seen in differential visibilities. Radiative-transfer modeling of Deneb, with allowance for stellar-wind mass loss, accounts fairly well for the observed decrease in the Halpha visibility. Based on the observed differential visibilities, we estimate that the mass-loss rate of Deneb has changed by less than 5%.
31 citations
1 Dec 2010
TL;DR: In this article, the spectral properties of luminous BA-type supergiants were derived from high-S/N and high-resolution spectra in the visual and near-IR.
Abstract: Context. Quantitative spectroscopy of luminous BA-type supergiants offers a high potential for modern astrophysics. Detailed studies allow the evolution of massive stars, galactochemical evolution, and the cosmic distance scale to be constrained observationally. Aims. A detailed and comprehensive understanding of the atmospheres of BA-type supergiants is required in order to use this potential properly. The degree to which we can rely on quantitative studies of this class of stars as a whole depends on the quality of the analyses for benchmark objects. We constrain the basic atmospheric parameters and fundamental stellar parameters, as well as chemical abundances of the prototype A-type supergiant Deneb to unprecedented accuracy by applying a sophisticated analysis methodology, which has recently been developed and tested. Methods. The analysis is based on high-S/N and high-resolution spectra in the visual and near-IR. Stellar parameters and abundances for numerous astrophysically interesting elements are derived from synthesis of the photospheric spectrum using a hybrid non-LTE technique, i.e. line-blanketed LTE model atmospheres and non-LTE line formation. Multiple metal ionisation equilibria and numerous hydrogen lines from the Balmer, Paschen, Brackett, and Pfund series are utilised simultaneously for the stellar parameter determination. The stellar wind properties are derived from Ha line-profile fitting using line-blanketed hydrodynamic non-LTE models. Further constraints come from matching the photospheric spectral energy distribution from the UV to the near-IR L band. Results. The atmospheric parameters of Deneb are tightly constrained: effective temperature T eff = 8525 ± 75 K, surface gravity logg = 1.10±0.05, microturbulence ξ = 8±1 km s -1 , macroturbulence, and projected rotational velocity v sin i are both 20±2 km s -1 . The abundance analysis gives helium enrichment by 0.10 dex relative to solar and an N/C ratio of 4.44 ± 0.84 (mass fraction), implying strong mixing with CN-processed matter. The heavier elements are consistently underabundant by ∼0.20 dex compared to solar. Peculiar abundance patterns, which were suggested in previous analyses cannot be confirmed. Accounting for non-LTE effects is essential for removing systematic trends in the abundance determination, for minimising statistical 1σ-uncertainties to ≤10-20% and for establishing all ionisation equilibria at the same time. Conclusions. A luminosity of (1.96±0.32)±10 5 L ⊙ , a radius of 203 ± 17 R ⊙ , and a current mass of 19±4 M ⊙ are derived. Comparison with stellar evolution predictions suggests that Deneb started as a fast-rotating late O-type star with M ZAMS ≃ 23 M ⊙ on the main sequence and is currently evolving to the red supergiant stage.
30 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2018 | 1 |
| 2015 | 1 |
| 2014 | 1 |
| 2013 | 1 |
| 2011 | 2 |
| 2010 | 6 |