Download THE SPECTRA OF FIVE IRREGULAR VARIABLE STARS George H

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 3^4 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 1948, by B. Kukarkin and P.
Parenago.
TABLE I
Variable Stars Observed
α
Star
SYCancri
EXLupi
V567 Sagittarii
YY Herculis
FN Sagittarii
(1900)
8* 55ψ4
15 56.3
17 55.8
18 10.3
18 48.0
Pg. Magnitude
Max.
Min.
δ
+18° 18'
-40 02
-36 39
+20 57
-19 07
10.9
11.4
13.5
11.1
9
13.8
13.4
14.5
<13.2
14
Spectral
Type
Pec.
Pd
Type of
Variation
RW Aur?
Nova-like
Irregular
Irregular
Nova-like
1. S Y Cancri.—Photometric observers1 have found large irregular variations, which sometimes were quite rapid. Ten spectrograms were obtained at the Lick Observatory in 1945, 1946,
and 1947 with dispersions of 130 A/mm and of 430 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 4471 and at the position of He ιι λ 4685.
1
R. Prager, A.N., 243, 364, 1931 ; P. Parenago, Nishni-Novgorod
(Gorki) Veränderliche Sterne, 4, 223, 1933 ; L. Jacchia, Beoh. Zirk., 18, 33,
1936.
211
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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 4233 Fe ιι
and probably λλ 4297, 4303 Fe ιι."
He concluded that "a con-
siderable 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 4 and 16, 1949, and one with the
Lick 36-inch refractor on May 14, 1950.
On these dates, the
visual magnitude of the variable was estimated as about 11.5.
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 4471. On the plate of February 4, 1949, 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, 1946.
3
A. EL Joy, ApJ., 102, 168, 1945; 110, 424, 1949.
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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 Andromedae, 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,4 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. Minkowski5
at Mount Wilson, who stated that, "This object is beyond doubt a
planetary nebula; whether it is actually variable should be investigated/'
Four slit spectrograms of V567 Sagittarii have been obtained
at Lick. The spectrum is certainly very similar to that of a planetary nebula, with strong bright lines on a weak continuum, and
with the intensities of λ 5006 and λ 4958 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. Wilson6 or as given
TABLE II
Emission Lines in V567 Sagittarii and FN Sagittarii
IntensityWave
Length
Identification
V567
Sgr
5015
5006
4958
4921
4861
4740
Τ/
XxJ
4713
4685
4471
He ι
[O in]
[O m]
i X & iι
He
Ηβ
[Α ιν]
JLJLCJ.
He ι
He π
He τ
100
50
···
20
2
·Φ·
4
3
4
5
Intensity
FN
Sgr
Wave
Length
Identification
2:
12
4
4
50
4387
4363
4340
4101
4026
3970
3967
3868
He ι
[Ο m]
Hy
Hb
Hei
Ηε
[Ne m]
[Nein]
5
20
4
V567
Sgr
4
8
5
1
5
5
FN
Sgr
2
7
20
15
2
4
1
Harvard Annals, 90, 221, 228, 1935.
Q
Pub. AS.P., 60, 386, 1948.
Ap.J., Ill, 279, 1950, Table 1.
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214
GEORGE H. HERBIG
by Miss Moore in the Revised Multiplet Table.7 The results are
contained in Table III.
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 observations and the fact that variability has not been detected in any
TABLE III
Radial Velocities of V567 Sagittarii
Date
June 22, 1946
July 23, 1946
July 16, 1947
June 3, 1950
Velocity from
Bright Lines
Weight
—62 km/sec
-78
-73
-63
1.9
2.0
1.8
1.7
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.
4. 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 4685 is nearly as strong as Ηβ.
The
[O in] line at λ 4363 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. 20,1945.
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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 1925.8 When the Lick spectrograms (listed in Table IV)
TABLE IV
Radial Velocities of FN Sagittarii
Date
June 22, 1946
May 14, 1950
July 15, 1950
Velocity from
Bright Lines
Weight
—74 km/sec
-52
-40
0.4
2.2
1.2
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.
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