Spectroscopic Luminosity Research Articles

The Abundance of Lithium in T Tauri Stars and Related Objects.

view Abstract Citations (82) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Abundance of Lithium in T Tauri Stars and Related Objects. Bonsack, Walter K. ; Greenstein, Jesse L. Abstract Spectrograms of four T Tauri stars involved in nebulosity and eight stars possibly similar in some respects to T Tauri stars have been examined for the presence of the resonance doublet of Li I at X 6708. A very strong feature at this wave length was found in the spectra of the four T Tauri stars and of SU Aur, which differs from Herbig's definition of the T Tauri class only in having a somewhat higher spectroscopic luminosity. Spectrophotometric analysis showed that the lithium/metals ratio in these five stars exceeds the solar ratio by a factor of 100 and approximately equals the terrestrial value. No Li I was detected in the other seven stars; except for the few hot stars included, these cannot then have lithium/metals ratios much in excess of the solar value These results suggest that young stars have approximately 1 lithium atom per 10 hydrogen atoms, at least in their atmospheres. Primary cosmic rays appear to be incapable of contaminating the interstellar medium, and then the entire protostar, with this amount of lithium. However, if a sufficiently efficient mechanism for the production of lithium at the surface of a star can be found, this result can be accomplished without the appearance of a large fraction of the star's energy as high-energy surface phenomena. The magnetic energy content of a protostar is sufficiently large that, if forced to the surface during the contraction and there dissipated in accelerating protons, the quantity of lithium required by the observations can be formed by spallation reactions in the atmosphere. Publication: The Astrophysical Journal Pub Date: January 1960 DOI: 10.1086/146810 Bibcode: 1960ApJ...131...83B full text sources ADS | data products SIMBAD (11)

Luminosities of the B stars from spectroscopic measurements

The problem of assigning distances to the B stars is reviewed and the development of the spectroscopic method briefly described. It is established that the strength of hydrogen line-absorption gives distances by indicating true luminosity. The Victoria work is a new calibration of which the chief features are: ( a) the hydrogen absorption is measured by spectrophotometric methods; and ( b) calibrating stars are drawn solely from galactic clusters, visual binaries, and eclipsing binaries. A correlation is found between absorption W and absolute visual magnitude M of the form M = −10·96 × 10 −0-.145 W . The system so defined agrees with that of the trigonometric parallaxes, with eclipsing binary luminosities, and with the moving-cluster luminosities of the Scorpio-Centaurus stream. Some applications are limited indicated and a first list of spectroscopic luminosities is given for 124 stars.

A POSSIBLE ENERGY SOURCE FOR T TAURI STARS

The emission spectra of the nebular variables of the Τ Tauri class, and of the related dwarf stars in dark nebulae, have been described by A. H. Joy.1»2 They are similar to the spectra of such disturbed regions of the sun as solar flares or the chromosphere. High-excitation lines are seen, such as He i, even He π, together with strong H, Ca n, Fe n, and some forbidden lines, superposed on an underlying late-type dwarf absorption spectrum. Joy,2 in his Table 2, remarks that in 11 out of 40 stars the absorption spectrum is partially or heavily obscured or filled in by a continuous emission. J. L. Greenstein3 found that the apparent luminosity of several of the Τ Tauri group (BD 6° 1253, R Mon, R CrA) was greater by about one magnitude than would be predicted from the spectroscopic luminosity, distance, and obscuration of the stars. For example, in spite of their location in dark lanes, the mean obscuration estimated by Joy2 is less than one magnitude. This is small compared to the total absorption in these dark clouds, and would not suggest the strong observed interaction of star and dense interstellar material.

Spectroscopic Luminosities of Stars of Types G and K in Two Selected Fields.

Spectroscopic Luminosities of Stars of Types G and K in Two Selected Fields.

A Quantitative Study of Certain Phases of F-Type Spectra

view Abstract Citations (4) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Quantitative Study of Certain Phases of F-Type Spectra Hynek, J. A. Abstract Quantitative data are given concerning the behavior of a number of the more im- portant lines in F spectra. These lines include members of many of the most important pairs used as luminosity criteria for the determination of spectroscopic parallaxes in the classical researches of the Mount Wilson Observatory. A discussion is given of the behavior of the various lines in each F subclass. Tue sharp- and diffuse-line F stars-A parameter (line width! line depth) is given as a measure of the diffuseness of the metallic lines exhibiting various degrees of rota- tional broadening. This parameter varies over a range of more than thirty times among stars of Draper type Fo. A comparison of Harvard and Mount Wilson spectral types shows that practically all of the bright diffuse-line Fo stars have been moved over into class A by Mount Wilson. The mean Mount Wilson spectral type of the twenty-one most diffuse H.D. Fo spectra is A 5.6. The intensities of Ca ii K and of H~ in sharp- and diffuse-line Fo stars confirm the consistency of the Henry Draper classification; at type Fo there is no systematic differ- ence in the intensities on passing from narrow- to broad-line stars. There is a tendency for the strong Fe i lines to be systematically fainter in the diffuse-line stars; it is possible, however, that this is due to systematic errors in measuring the equivalent widths. The sharp drop in the number of rapidly rotating stars between Fo and F5 is con- firmed, and it is shown that the diffuse-line stars are distributed over a considerably smaller range of spectroscopic absolute magnitude than are those having sharp lines. For sharp-line Fo stars the range is approximately 5 mag.; for twenty-one of the most diffuse-line Fo stars it is 0.9 mag., the latter clustering about absolute magnitude + 2.0. The effect is not so pronounced when trigonometric absolute magnitudes are used, and it is possible that the difference is a result of a systematic error in the determination of spectroscopic parallaxes for rapidly rotating stars. The behavior of Ca n K and of H~ with changes in spectral type-A brief quantita- tive discussion of some of the most prominent F-type classification criteria is given. Ca ii K increases in intensity about 50 per cent from Fo to Go and H~ dçcreases 75 per cent in the same range. The ratio K/Ho increases from 0.7 at Fo to 3.8 at Go. Visual estimates of this ratio are usually given as considerably greater; this difference between measured and visual estimates is ascribed to the effect on the estimates of the Stark broadening of H6. The behavior of the luminosity criteria.-Equivalent widths in approximately one hundred F stars are given for the individual lines of five line ratios which have been used in the determination of spectroscopic luminosities at Mount Wilson. A quantita- tive summary is given of the behavior of these line ratios with luminosity in the F subdivisions. At type F5 the most sensitive criteria among those discussed are: Fe ii- Fei 4233/Fe 14235 and Sc 114246/Fe 14250; at F8: Fei 4o71/Sr u 4077 and Tiii- Zrr14161/Mg14167;atGo: Fe14o71/Srn4o77 and Sr114215/Fe1425o. The variation of Ca i and Fe i with luminosity at F8 and Go-The lines Ca I 4226 and Fe i 4045 vary with luminosity in a peculiar manner at types F8 and Go. Both lines are very strong at M= +4.5. They then decrease in intensity to M= +3.3. In the giants, however, both ]ines are strengthened with increasing luminosity. In the case of Ca I 4226 the intensity reaches a maximum and is identical in dwarfs (M= +4.5) and in the most luminous giants (M= -3.5). For intermediate luminosities the line has only one-third of its maximum intensity. Its range in equivalent width is from 1.5 to 0.5 A Publication: The Astrophysical Journal Pub Date: November 1935 DOI: 10.1086/143683 Bibcode: 1935ApJ....82..338H full text sources ADS |