2007A&A...468..263C


Query : 2007A&A...468..263C

2007A&A...468..263C - Astronomy and Astrophysics, volume 468, 263-272 (2007/6-2)

Fundamental parameters of He-weak and He-strong stars.

CIDALE L.S., ARIAS M.L., TORRES A.F., ZOREC J., FREMAT Y. and CRUZADO A.

Abstract (from CDS):

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. 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. 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. 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 ±0.3mag for He-weak stars, while it is ±0.5mag 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.

Abstract Copyright:

Journal keyword(s): stars: early-type - stars: chemically peculiar - stars: magnetic fields - stars: fundamental parameters

Simbad objects: 29

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Number of rows : 29
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 * alf Scl Ro* 00 58 36.3593029 -29 21 26.824714 3.52 4.09 4.27 4.30 4.43 B7IIIp 246 0
2 * tet Hyi ** 03 02 15.4488409848 -71 54 08.839047780   5.365 5.499     B8III/IV 91 0
3 * 20 Eri a2* 03 36 17.4041095200 -17 28 01.472307996 4.61 5.10 5.23     B8/9III 170 0
4 * 22 Eri a2* 03 40 38.3331139440 -05 12 38.555731188 4.81 5.38 5.53     B9IIIpSi4200 123 0
5 * 20 Tau PM* 03 45 49.6065620 +24 22 03.886360 3.40 3.80 3.87 3.85 3.90 B8III 417 1
6 HD 28843 Ro* 04 32 37.5537339576 -03 12 34.344832032 5.13 5.67 5.81     B9III 128 0
7 V* V1046 Ori SB* 05 35 21.8667428568 -04 29 39.024375324 5.66 6.43 6.56 6.61 6.74 B2/3V 289 0
8 * sig Ori E Y*O 05 38 47.2050040320 -02 35 40.521424812 5.66 6.38 6.46 6.84 7.08 B2IV-Vp_He 424 0
9 V* V901 Ori Ro* 05 40 56.3704617744 -01 30 25.856677224 5.96 6.82 6.96     B2V 315 2
10 * 12 CMa a2* 06 47 01.4835271104 -21 00 55.451696472 5.27 5.89 6.08     B7II/III 136 0
11 HD 264111 * 06 47 53.8569554424 +04 40 00.850904832 9 9.64 9.57     ~ 49 0
12 * 33 Gem Ro* 06 49 49.8362378064 +16 12 10.382708016 5.24 5.72 5.87     B7III 141 0
13 * 40 Gem ** 06 59 27.9326561760 +25 54 50.987089260 5.71 6.280 6.397     B8VpSi 81 0
14 * ups02 Pup Be* 07 18 38.1853955232 -36 44 33.854932104 4.28 4.95 5.11 5.17 5.38 B3Vne 109 1
15 HD 58260 * 07 23 19.5997521648 -36 20 24.538554852 5.87 6.61 6.73     B2/3Vp 94 0
16 HD 60344 * 07 33 02.1373084440 -23 56 03.348474360 6.71 8.49 9.09 8.62   B2III 73 0
17 HD 64740 * 07 53 03.6353775 -49 36 46.952967 3.48 4.40 4.63 4.76 4.97 B2V 197 0
18 HD 66765 ** 08 02 55.7155901784 -48 19 29.981984880 5.69 6.470 6.624     B1/2V 38 0
19 HD 74196 Ce* 08 40 17.4649643448 -53 00 55.430609904 4.97 5.47 5.61     B9/A0 127 0
20 * a Cen Ro* 14 23 02.2390294 -39 30 42.549250 3.50 4.24 4.42 4.53 4.70 B2V 263 0
21 * 3 Sco Ro* 15 54 39.5296532472 -25 14 37.459966128 5.23 5.81 5.87     B8III/IV 201 0
22 V* V913 Sco Ro* 15 58 34.8665694960 -24 49 53.361727284 4.70 5.34 5.43     B5V 192 0
23 HD 144334 ** 16 06 06.3891324384 -23 36 22.849641396 5.29 5.84 5.92     B8V 184 0
24 HD 144661 * 16 07 51.8878572504 -24 27 44.447463108 5.74 6.27 6.33     B8IV/V 150 0
25 HD 144844 V* 16 08 43.7202865416 -23 41 07.483461252 5.59 5.90 5.88     B9V 146 0
26 V* V957 Sco Ro* 17 52 13.6613130072 -34 47 57.109291728 5.16 5.80 5.90     B6Ib 129 0
27 V* V686 CrA a2* 18 56 40.4859327624 -37 20 35.701261512 4.53 5.24 5.38     B3V 199 0
28 * 30 Cap * 21 17 57.2864746704 -17 59 06.499058280   5.263 5.383     B5II/III 85 0
29 NAME Gould Belt PoG ~ ~           ~ 797 1

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2022.05.21-23:47:30

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