THE SPECTRA OF FIVE IRREGULAR VARIABLE STARS. George H. Herbig Lick Observatory, University of California

Transcription

1 THE SPECTRA OF FIVE IRREGULAR VARIABLE STARS George H. Herbig Lick Observatory, University of California The spectra of the five irregular variables listed in Table I have been obtained mainly with the 2-prism spectrograph of the 36-inch refractor and a camera of 3^ inches focal length, a combination which gives a dispersion of 130 A/mm at Hy. The spectra of four of these stars are reproduced in Plate XVII. The information contained in Table I was taken from the General Catalogue oj Variable Stars for 198, by B. Kukarkin and P. Parenago. TABLE I Variable Stars Observed Star α (1900) δ Pg. Magnitude Max. Min. Spectral Type Type of Variation SYCancri 8* 55ψ ' EXLupi V567 Sagittarii YY Herculis <13.2 FN Sagittarii Pec. Pd RW Aur? Nova-like Irregular Irregular Nova-like 1. S Y Cancri. Photometric observers 1 have found large ir- regular variations, which sometimes were quite rapid. Ten spec- trograms were obtained at the Lick Observatory in 195, 196, and 197 with dispersions of 130 A/mm and of 30 A/mm. When the variable is near maximum the energy distribution in the continuous spectrum of SY Cancri in the photographic region is like that of an early-type star. The only absorption features are very broad, shallow lines of hydrogen and very faint, wide lines of He i. Weak emission cores are present near the centers of and Hy. When the star is faint, these cores appear as strong, hazy bright lines, and emission can be seen in still higher members of the Balmer series. Emission is present at this time also in He ι λ 71 and at the position of He ιι λ R. Prager, A.N., 23, 36, 1931 ; P. Parenago, Nishni-Novgorod (Gorki) Veränderliche Sterne,, 223, 1933 ; L. Jacchia, Beoh. Zirk., 18, 33,

2 212 GEORGE H. HERBIG The spectrum and its changes are reminiscent of such stars as S S Cygni, CN Orionis, and Ζ Camelopardalis. This similarity, combined with our limited knowledge of the character of the light-variation, suggests that SY Cancri resembles more closely the objects typified by the latter two stars rather than any other well-known group of irregular variables. 2. EX Lupi. The variations in light of EXLupi (HV11976) were studied by D. B. McLaughlin on Harvard plates. 2 He found that the star exhibited nova-like activity of small amplitude on several occasions, as well as minor irregular fluctuations. One objective prism plate showed "a strong continuous spectrum [with] superimposed weak emission lines of hydrogen, very strong bright Η and Κ of Ca n, and faint emission at λ 233 Fe ιι and probably λλ 297, 303 Fe ιι." He concluded that "a considerable resemblance to Ζ Andromedae, in both spectrum and light variation, is suggested." Three slit spectrograms of EX Lupi have been obtained : two with the Cassegrain spectrograph of the 82-inch McDonald reflector (with the Gf/1 combination, which gives a dispersion of 150 A/mm at Hy) on February and 16, 199, and one with the Lick 36-inch refractor on May 1, On these dates, the visual magnitude of the variable was estimated as about These plates show strong, slightly diffuse, bright lines of Η and Ca il on a continuum whose energy distribution suggests an earlytype star, although no absorption lines can be seen with certainty. Several of the strongest Fe n lines are present, as well as a very faint He ι λ 71. On the plate of February, 199, strong longward absorption fringes, with a displacement of +250 km/sec, are present at the Η and Can lines, but they are not visible on the other spectrograms. The bright Κ line is displaced about 65 km/sec to longward with respect to the hydrogen emission. The spectral characteristics of EX Lupi are best matched among the irregular variables by certain of the emission-line objects associated with the dark clouds in Taurus. 3 For example, BP Tauri, except for stronger He i, has a spectrum very similar 2 AJ., 52, 109, A. EL Joy, ApJ., 102, 168, 195; 110, 2, 199.

3 SPECTRA OF FIVE IRREGULAR VARIABLES 213 to that of EX Lupi. The analogy is strengthened by the fact that EX Lupi is projected upon the same dark cloud that contains the well-known Τ Tauri variable RU Lupi. Consequently, unless EX Lupi in the future develops high excitation characteristics, which would identify it with nova-like variables such as Ζ An- dromedae, it seems most reasonable to classify it among the emission objects associated with nebulosity. 3. V567 Sagittarii. This object was discovered by Miss Henrietta Swope, who stated : "The spectrum is given as Pd in Harvard Circular 231, where it is called a gaseous nebula.... The variation is real and apparently irregular with no distinctive character.,, This object has also been observed by R. Minkowski 5 at Mount Wilson, who stated that, "This object is beyond doubt a planetary nebula; whether it is actually variable should be in- vestigated/' Four slit spectrograms of V567 Sagittarii have been obtained at Lick. The spectrum is certainly very similar to that of a plane- tary nebula, with strong bright lines on a weak continuum, and with the intensities of λ 5006 and λ 958 much greater than the intensity of //β. The emission lines observed, together with their estimated intensities, are listed in Table II. Radial velocities have been obtained from the four spectrograms using the normal wave lengths of the bright lines as derived by O. C. Wilson 6 or as given TABLE II Emission Lines in V567 Sagittarii and FN Sagittarii Wave Identifi- V567 Length cation Sgr Intensity- FN Sgr 5015 He ι 2: 5006 [O in] [O m] He i X & i ι Ηβ [Α ιν] 2 Τ/ 713 XxJ JLJLCJ. He ι Φ He π He τ 3 Wave Identifi- V567 Length cation Sgr 387 He ι 363 [Ο m] 30 Hy Hb Hei 3970 Ηε [Ne m] [Nein] 5 Intensity Harvard Annals, 90, 221, 228, Pub. AS.P., 60, 386, 198. Q Ap.J., Ill, 279, 1950, Table 1. FN Sgr

4 21 GEORGE H. HERBIG by Miss Moore in the Revised Multiplet Table. 7 contained in Table III. The results are There is no evidence for variation of the radial velocity or of the spectrum. Furthermore, the visual magnitude of the object was always the same, as nearly as could be estimated at the finder, when the spectrograms were obtained. In view of these observa- tions and the fact that variability has not been detected in any TABLE III Radial Velocities of V567 Sagittarii Velocity from Date Bright Lines Weight June 22, km/sec 1.9 July 23, July 16, June 3, Weighted mean V = 69 ± 3 (p.e.) km/sec other planetary nebula, it would seem probable that the object is not a variable. Miss Swope's estimates depend upon plates obtained with Harvard photographic refractors. It might be worth while to examine other such plates showing nearly stellar planetaries in order to see if the light-variations reported for V567 Sagittarii can be accounted for as an instrumental effect.. Y Y H er culis. Little is known about the variations of this star except that the changes seem to be irregular and rather slow. Spectra were obtained on May 20 and June 3, 1950, when the variable was of visual magnitude 13. These plates show a strong emission spectrum superimposed upon a late-type absorption spectrum with moderately strong TiO bands, corresponding to a type of about M2. The hydrogen lines //ß, Hy, and are visible in emission, and He ιι λ 685 is nearly as strong as Ηβ. The [O in] line at λ 363 is present, as well as a faint He ιλαατι. The velocity displacements of the bright lines on the two spectrograms differ by 27 km/sec, an amount considerably larger than one would expect from errors of measurement. There is no doubt 7 Princeton Contr. No. 20,195.

5 SPECTRA OF FIVE IRREGULAR VARIABLES 215 that YY Herculis belongs to the small group of variable stars with combination spectra, such as AX Persei, CI Cygni, and Ζ Andromedae. S. FN Sagittarii. This star has been classified as "novalike'' on the strength of a flare-up to magnitude 9 that was observed in When the Lick spectrograms (listed in Table IV) TABLE IV Radial Velocities of FN Sagittarii Velocity from Date Bright Lines Weight June 22, km/sec 0. May 1, July 15, Weighted mean V = 51 ± 5 (p.e.) km/sec were taken, the variable was near visual magnitude 13 ; small variations in the light are still taking place. These plates show a bright-line spectrum on a weak continuum, of a character which is not atypical for an old nova. The individual lines, together with their estimated intensities, are given in Table IL 8 S. Beljawsky, A.N., 230, 153, 1927 ; C. H. Payne, Harv. Bull. 861, 1928.