Fundamental parameters of He-weak and He-strong stars
- Autores
- Cidale, Lydia Sonia; Arias, María Laura; Torres, Andrea Fabiana; Zorec, J.; Frémat, Y.; Cruzado, Alicia
- Año de publicación
- 2007
- Idioma
- inglés
- Tipo de recurso
- artículo
- Estado
- versión publicada
- Descripción
- Context. He-weak and He-strong stars are chemically peculiar AB objects whose He lines are anomalously weak or strong for their MK spectral type. The determination of fundamental parameters for these stars is often more complex than for normal stars due to their abundance anomalies. Aims. We discuss the determination of fundamental parameters: effective temperature, surface gravity, and visual and bolometric absolute magnitudes of He-weak and He-strong stars. We compare our values with those derived independently from methods based on photometry and model fitting. Methods. We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 Å of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. This system is based on the measurement of the continuum energy distribution around the Balmer discontinuity (BD). For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their Teff determination. Results. We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the HIPPARCOS parallaxes and the BCD values is on average ±0.3 mag for He-weak stars, while it is ±0.5 mag for He-strong stars. For He-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of Teff. By means of model atmosphere calculations with enhanced He/H abundance ratios we show that larger He/H ratios produce smaller BD which naturally explains the Teff overestimation. We take advantage of these calculations to introduce a method to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479 suggests that the Teff of this star remains fairly constant as the star spectrum undergoes changes in the intensity of H and He absorption lines. Data for the He-strong star HD 66765 are reported for the first time.
Facultad de Ciencias Astronómicas y Geofísicas - Materia
-
Ciencias Astronómicas
Stars: chemically peculiar
Stars: early-type
Stars: fundamental parameters
Stars: magnetic fields - Nivel de accesibilidad
- acceso abierto
- Condiciones de uso
- http://creativecommons.org/licenses/by-nc-sa/4.0/
- Repositorio
- Institución
- Universidad Nacional de La Plata
- OAI Identificador
- oai:sedici.unlp.edu.ar:10915/83124
Ver los metadatos del registro completo
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Fundamental parameters of He-weak and He-strong starsCidale, Lydia SoniaArias, María LauraTorres, Andrea FabianaZorec, J.Frémat, Y.Cruzado, AliciaCiencias AstronómicasStars: chemically peculiarStars: early-typeStars: fundamental parametersStars: magnetic fieldsContext. He-weak and He-strong stars are chemically peculiar AB objects whose He lines are anomalously weak or strong for their MK spectral type. The determination of fundamental parameters for these stars is often more complex than for normal stars due to their abundance anomalies. Aims. We discuss the determination of fundamental parameters: effective temperature, surface gravity, and visual and bolometric absolute magnitudes of He-weak and He-strong stars. We compare our values with those derived independently from methods based on photometry and model fitting. Methods. We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 Å of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. This system is based on the measurement of the continuum energy distribution around the Balmer discontinuity (BD). For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their T<SUB>eff</SUB> determination. Results. We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the HIPPARCOS parallaxes and the BCD values is on average ±0.3 mag for He-weak stars, while it is ±0.5 mag for He-strong stars. For He-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of T<SUB>eff</SUB>. By means of model atmosphere calculations with enhanced He/H abundance ratios we show that larger He/H ratios produce smaller BD which naturally explains the T<SUB>eff</SUB> overestimation. We take advantage of these calculations to introduce a method to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479 suggests that the T<SUB>eff</SUB> of this star remains fairly constant as the star spectrum undergoes changes in the intensity of H and He absorption lines. Data for the He-strong star HD 66765 are reported for the first time.Facultad de Ciencias Astronómicas y Geofísicas2007info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionArticulohttp://purl.org/coar/resource_type/c_6501info:ar-repo/semantics/articuloapplication/pdf263-272http://sedici.unlp.edu.ar/handle/10915/83124enginfo:eu-repo/semantics/altIdentifier/issn/0004-6361info:eu-repo/semantics/altIdentifier/doi/10.1051/0004-6361:20066454info:eu-repo/semantics/openAccesshttp://creativecommons.org/licenses/by-nc-sa/4.0/Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)reponame:SEDICI (UNLP)instname:Universidad Nacional de La Platainstacron:UNLP2025-09-29T11:15:41Zoai:sedici.unlp.edu.ar:10915/83124Institucionalhttp://sedici.unlp.edu.ar/Universidad públicaNo correspondehttp://sedici.unlp.edu.ar/oai/snrdalira@sedici.unlp.edu.arArgentinaNo correspondeNo correspondeNo correspondeopendoar:13292025-09-29 11:15:42.163SEDICI (UNLP) - Universidad Nacional de La Platafalse |
dc.title.none.fl_str_mv |
Fundamental parameters of He-weak and He-strong stars |
title |
Fundamental parameters of He-weak and He-strong stars |
spellingShingle |
Fundamental parameters of He-weak and He-strong stars Cidale, Lydia Sonia Ciencias Astronómicas Stars: chemically peculiar Stars: early-type Stars: fundamental parameters Stars: magnetic fields |
title_short |
Fundamental parameters of He-weak and He-strong stars |
title_full |
Fundamental parameters of He-weak and He-strong stars |
title_fullStr |
Fundamental parameters of He-weak and He-strong stars |
title_full_unstemmed |
Fundamental parameters of He-weak and He-strong stars |
title_sort |
Fundamental parameters of He-weak and He-strong stars |
dc.creator.none.fl_str_mv |
Cidale, Lydia Sonia Arias, María Laura Torres, Andrea Fabiana Zorec, J. Frémat, Y. Cruzado, Alicia |
author |
Cidale, Lydia Sonia |
author_facet |
Cidale, Lydia Sonia Arias, María Laura Torres, Andrea Fabiana Zorec, J. Frémat, Y. Cruzado, Alicia |
author_role |
author |
author2 |
Arias, María Laura Torres, Andrea Fabiana Zorec, J. Frémat, Y. Cruzado, Alicia |
author2_role |
author author author author author |
dc.subject.none.fl_str_mv |
Ciencias Astronómicas Stars: chemically peculiar Stars: early-type Stars: fundamental parameters Stars: magnetic fields |
topic |
Ciencias Astronómicas Stars: chemically peculiar Stars: early-type Stars: fundamental parameters Stars: magnetic fields |
dc.description.none.fl_txt_mv |
Context. He-weak and He-strong stars are chemically peculiar AB objects whose He lines are anomalously weak or strong for their MK spectral type. The determination of fundamental parameters for these stars is often more complex than for normal stars due to their abundance anomalies. Aims. We discuss the determination of fundamental parameters: effective temperature, surface gravity, and visual and bolometric absolute magnitudes of He-weak and He-strong stars. We compare our values with those derived independently from methods based on photometry and model fitting. Methods. We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 Å of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. This system is based on the measurement of the continuum energy distribution around the Balmer discontinuity (BD). For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their T<SUB>eff</SUB> determination. Results. We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the HIPPARCOS parallaxes and the BCD values is on average ±0.3 mag for He-weak stars, while it is ±0.5 mag for He-strong stars. For He-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of T<SUB>eff</SUB>. By means of model atmosphere calculations with enhanced He/H abundance ratios we show that larger He/H ratios produce smaller BD which naturally explains the T<SUB>eff</SUB> overestimation. We take advantage of these calculations to introduce a method to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479 suggests that the T<SUB>eff</SUB> of this star remains fairly constant as the star spectrum undergoes changes in the intensity of H and He absorption lines. Data for the He-strong star HD 66765 are reported for the first time. Facultad de Ciencias Astronómicas y Geofísicas |
description |
Context. He-weak and He-strong stars are chemically peculiar AB objects whose He lines are anomalously weak or strong for their MK spectral type. The determination of fundamental parameters for these stars is often more complex than for normal stars due to their abundance anomalies. Aims. We discuss the determination of fundamental parameters: effective temperature, surface gravity, and visual and bolometric absolute magnitudes of He-weak and He-strong stars. We compare our values with those derived independently from methods based on photometry and model fitting. Methods. We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 Å of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. This system is based on the measurement of the continuum energy distribution around the Balmer discontinuity (BD). For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their T<SUB>eff</SUB> determination. Results. We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the HIPPARCOS parallaxes and the BCD values is on average ±0.3 mag for He-weak stars, while it is ±0.5 mag for He-strong stars. For He-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of T<SUB>eff</SUB>. By means of model atmosphere calculations with enhanced He/H abundance ratios we show that larger He/H ratios produce smaller BD which naturally explains the T<SUB>eff</SUB> overestimation. We take advantage of these calculations to introduce a method to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479 suggests that the T<SUB>eff</SUB> of this star remains fairly constant as the star spectrum undergoes changes in the intensity of H and He absorption lines. Data for the He-strong star HD 66765 are reported for the first time. |
publishDate |
2007 |
dc.date.none.fl_str_mv |
2007 |
dc.type.none.fl_str_mv |
info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Articulo http://purl.org/coar/resource_type/c_6501 info:ar-repo/semantics/articulo |
format |
article |
status_str |
publishedVersion |
dc.identifier.none.fl_str_mv |
http://sedici.unlp.edu.ar/handle/10915/83124 |
url |
http://sedici.unlp.edu.ar/handle/10915/83124 |
dc.language.none.fl_str_mv |
eng |
language |
eng |
dc.relation.none.fl_str_mv |
info:eu-repo/semantics/altIdentifier/issn/0004-6361 info:eu-repo/semantics/altIdentifier/doi/10.1051/0004-6361:20066454 |
dc.rights.none.fl_str_mv |
info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by-nc-sa/4.0/ Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) |
eu_rights_str_mv |
openAccess |
rights_invalid_str_mv |
http://creativecommons.org/licenses/by-nc-sa/4.0/ Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) |
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