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Ultraviolet photometry from the Orbiting Astronomical Observatory. XXIII - The resonance lines of triply ionized carbon and silicon in the spectra of hot stars

1976; IOP Publishing; Volume: 206; Linguagem: Inglês

10.1086/154368

1538-4357

R. J. Panek, Blair D. Savage,

Astronomy and Astrophysical Research

view Abstract Citations (45) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet photometry from the Orbiting Astronomical Observatory. XXIII. The resonance lines of triply ionized carbon and silicon in the spectra of hot star. Panek, R. J. ; Savage, B. D. Abstract Quantitative measurements of the absorption strength of the Si iv (1400 A) and C iv (1550 A) resonance doublets have been made from OAO-2 far-ultraviolet spectra of 118 0- and B-type stars. These lines are generally very strong and a useful measure of their strength can be made even though the OAO-2 scans have relatively low spectral resolution (FWHM = 12 A). However, variable amounts of line blending limit the accuracy of the results to approximately I 1 to 2 A in the equivalent width. For dwarf stars the strength of both features correlates well with spectral type or temperature. The Si iv doublet peaks in strength near spectral type Bl with a total equivalent width of about 5 A in agreement with the theoretical non-LTE (NLTE) plane-parallel static models of Kamp. The C iv doublet in dwarfs rapidly increases in strength from B2 to BO and attains an equivalent width of about S A at spectral type 09. For both doublets we note a large increase in the absorption equivalent width with luminosity classification, the increase amounting to a factor of 2 to 3 between dwarfs and supergiants. In the luminous 0 stars we also note a change in the line profile to the P Cygni type. In the case of the Si iv line for stars cooler than spectral type B0.5 the observed luminosity effect is roughly consistent with the predictions of static NLTE models. However, for the 0 stars the static models predict a decrease in equivalent width with increasing luminosity. The differences between theory and observation are associated with the effects of mass outflow. The observations include a number of B stars with peculiar visual spectra. With the exception of 0 Car, which exhibits an abnormally weak C iv line, the various peculiar stars observed appear to have normal Si iv and C iv line strengths. For a group of rapidly rotating stars the C iv line appears marginally stronger than expected on the basis of MK classification, while Si iv appears normal. In the case of the Be shell star, y Cas, we have noted a factor of 2 increase in the strength of Si iv and C iv over a time scale of months. With the exception of ` CMa and fl Cep, the Si iv and C iv lines in a group of 11 p Cephei variables appear to have strengths consistent with their MK classification. A number of repeated observations of bright early-type stars were searched for absorption line variability on time scales ranging from minutes to years. With only a few exceptions no variability was found. The sample included a number of luminous 0 supergiants, suggesting that the mass loss from these objects occurs as a steady process. Subject headings: stars: early-type stars: spectral classification - ultraviolet: spectra Publication: The Astrophysical Journal Pub Date: May 1976 DOI: 10.1086/154368 Bibcode: 1976ApJ...206..167P Keywords: Carbon; Early Stars; Hot Stars; Silicon; Stellar Spectrophotometry; Ultraviolet Photometry; Astronomical Catalogs; B Stars; Dwarf Stars; Far Ultraviolet Radiation; O Stars; Oao 2; Astronomy full text sources ADS | data products SIMBAD (121) Related Materials (37) Part 1: 1970ApJ...161..377C Part 2: 1972ApJ...171..293B Part 3: 1972ApJ...172..755W Part 4: 1972ApJ...178..727D Part 5: 1972ApJ...178..189B Part 6: 1972ApJ...178..495D Part 7: 1973ApJ...179..527M Part 8: 1973ApJ...185..577L Part 9: 1973ApJ...185..921E Part 10: 1974ApJ...189..303G Part 11: 1974ApJ...187..521D Part 12: 1973ApJ...186..939H Part 13: 1974ApJ...187..197S Part 14: 1974ApJ...187..243J Part 15: 1974ApJ...190..319L Part 16: 1974ApJ...191..659S Part 17: 1975ApJ...195..121D Part 18: 1975ApJ...197..379E Part 19: 1975ApJ...199...92S Part 20: 1976ApJ...203..410B Part 21: 1976Ap&SS..41..121K Part 23: 1976ApJ...208..135L Part 24: 1976ApJ...208...64L Part 25: 1979ApJ...228...95C Part 26: 1977ApJ...211..207H Part 27: 1978ApJ...219..947L Part 28: 1978ApJ...222..909W Part 29: 1978ApJ...220..582E Part 30: 1979ApJS...39..195C Part 31: 1979ApJ...229..994G Part 32: 1980ApJS...43..501C Part 33: 1979ApJ...228..419W Part 34: 1980ApJ...236..798W Part 35: 1980ApJS...42..283M Part 36: 1984ApJ...281..774C Part 37: 1982ApJ...256....1C Part 38: 1982AJ.....87..849D