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Properties of He-rich stars. II. CNO abundances and projected rotational velocities
We present an abundance analysis of light elements in the most massivechemically peculiar (CP) stars, He-rich stars. The analysis is based onboth low and high-resolution observations collected at ESO, La Silla,Chile in the optical region and includes 6 standard and 21 He-richstars. Light element abundances display a diverse pattern fromunder-solar up to above-solar values. Carbon is found underabundant inthe hottest He-rich stars and normal in the coolest ones, according tothe LTE model predictions. The distribution of projected rotationalvelocities shows a significant excess of slow rotators, no He-rich starshaving vsin i > 130 km s(-1) . Based on observations collected at theEuropean Southern Observatory, La Silla, Chile (programmes 7-043 and7-010 of periods 49 and 50 resp.)
| Light element abundances in He-rich stars
We present an abundance analysis of light elements in He-rich stars. Theanalysis is based on both low and high resolution observations collectedat ESO, La Silla, Chile in the optical region and includes 6 standardsand 21 He-rich stars. Light-element abundances display a diversepattern: they range from under-solar up to above-solar values.
| Age variation of helium abundance in He-rich stars.
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| Properties of He-rich stars. I. Their evolutionary state and helium abundance.
A determination of the surface gravity and an abundance analysis ofhelium in a sample of 17 He-rich and 5 normal, reference stars ispresented. These results are derived from low resolution CCD spectra,but each star was measured at least 6 times in order to obtain asignificant average spectrum for the spectroscopic variables. The heliumabundances derived from the models used are very close to 0.1 fornormal, reference stars and are larger for the others, clearlyindicating the He-rich phenomenon in them. NLTE effects, errors on themicroturbulence value or on the surface gravity do not influence theestimated helium abundances. Nevertheless, synthesized Geneva coloursare affected by the He-rich peculiarity, especially the [U-B] indexwhich systematically changes by -0.025 mag per 0.1 of He abundance forthe coolest stars in the sample. We cannot confirm the correlationbetween the evolutionary state and the helium abundance reportedpreviously (Zboril et al. 1994, International Conference on CP andMagnetic Stars.", Tatranska Lomnica, eds. J. Zverko and J. Ziznovsky, p.105), although we used a more reliable technique of log(g)determination. All He-rich objects lie within the main sequence: theirsurface gravities are all inside the range 4.1
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| A new list of effective temperatures of chemically peculiar stars. II.
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| Radio emission from chemically peculiar stars
In five VLA observing runs the initial survey of radio emission frommagnetic Bp-Ap stars by Drake et al. is extended to include a total of16 sources detected at 6 cm out of 61 observed, giving a detection rateof 26 percent. Of these stars, three are also detected at 2 cm, four at3.6 cm, and five at 20 cm. The 11 new stars detected as radio sourceshave spectral types B5-A0 and are He-weak and Si-strong. No classical(SrCrEu-type) Ap stars have yet been detected. The 16 detected sourcesshow a wide range of radio luminosities with the early-B He-S stars onaverage 20 times more radio luminous than the late-B He-W stars and 1000times more luminous than Theta Aurigae. Multifrequency observationsindicate flat spectra in all cases. Four stars have a detectable degreeof circular polarization at one or more frequencies. It is argued thatthe radio-emitting CP (chemically peculiar) stars form a distinct classof radio stars that differs from both the hot star wind sources and theactive late-type stars. The observed properties of radio emission fromthese stars may be understood in terms of optically thickgyrosynchrotron emission from a nonthermal distribution of electronsproduced in a current sheet far from the star. In this model theelectrons travel along magnetic fields to smaller radii and highermagnetic latitudes where they mirror and radiate microwave radiation.
| On dependence of helium abundance upon magnetic field in He-r stars.
Not Available
| The Relation Between Magnetic Field Strength and Helium Abundance in Helium Rich Stars
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| The discovery of nonthermal radio emission from magnetic Bp-Ap stars
In a VLA survey of chemically peculiar B- and A-type stars with strongmagnetic fields, five of the 34 stars observed have been identified as 6cm continuum sources. Three of the detections are helium-strong early Bpstars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak,silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452,Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) rangefrom log L6 = 16.2 to 17.9, somewhat less than the OB supergiants andW-R stars. Three-frequency observations indicate that the helium-strongBp stars are variable nonthermal sources.
| On the Effective Temperatures of Chemically Peculiar Stars
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| Observational problems of investigation of stars with anomalous helium lines.
Not Available
| A survey of spectral morphology and rotational velocities among the helium-rich stars
A spectroscopically homogeneous listing of all known members of thehelium-rich B star category is presented together with uniform estimatesof their rotational velocities. Equivalent widths of hydrogen, helium,and metal lines in the spectra of the helium-rich and comparison starsare given. The distribution of rotational velocities is found to beindistinguishable from that of normal early B dwarfs, except for apossible excess of rapid rotators. The existence of metal abundanceanomalies in the helium-rich spectra is critically discussed, as is theidentification of helium-rich stars as massive Population I objects withnormal main sequence cores and surface helium enhancements, or as lowmass highly evolved objects with processed cores.
| Spectral atlas of helium-rich stars
An atlas of coude spectra of 33 helium-rich O- and B-stars and 11comparison stars in the 3700-4600 A spectral range is presented. Theatlas comprises stars with temperatures from 10,000 to 60,000 deg K inwhich He lines are visible in the spectra, and includes variable Hestars; stars with spectral types O8 to B5 and magnitudes (m(v)) lessthan or equal to 11.0 are considered. The purpose of the atlas is togive a sample of spectra in which, from the observational point of view,the differences caused by certain physical parameters includingeffective temperature, logarithm of the gravity and observed rotationalvelocity, can be judged by eye. Mechanisms for He enrichment in theatmosphere are also discussed.
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Observation and Astrometry data
| Constellation: | Gemini |
| Right ascension: | 06h37m46.71s |
| Declination: | +12°46'05.1" |
| Apparent magnitude: | 9.15 |
| Proper motion RA: | -0.6 |
| Proper motion Dec: | -2 |
| B-T magnitude: | 9.241 |
| V-T magnitude: | 9.158 |
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