Non-Periodic Phenomena in Variable Stars
IAU Colloquium, Budapest, 1968
SPECTROSCOPIC VARIATIONS IN WY GEM, W CEP AND HD 4174
A. MAMMANO
Astrophysical Observatory, Asiago
A. MARTINI
Astrophysical Laboratory, Frascati
Some late-type stars with forbidden lines, suspected to be binaries or
to have combination spectra, are under observation at Asiago. In this
paper the preliminary results for WY Gem, W Cep and HD 4174 are presented.
WY Gem (= HD 42474) was classified by Bidelman (1954) as VV Cep type
star. The available spectral classifications are: Harvard (HD): K5;
Adams et al. (1935): M3ep; Swings and Struve (1940): M3ep + B3; Bidelman
(1954): M2ep Iab + B.
The best description of the WY Gem spectrum is that of Swings and Struve
(1940) who found an ultraviolet region "free from the late-type spectrum"
and showing broad Balmer absorption lines, down to H8, with sharp centers.
Moreover, they found the CaII (K) line "sharp and narrow" and a strong line
at 3819 A (probably HeI).
At present, the late-type absorption spectrum is that of a normal M0
supergiant whose strong continuous spectrum masks the emissions in the
visual region and falls off below 4000 A. The Balmer absorption lines
(from Hbeta to H9 on our plates) are narrow and, with the exception of Hbeta,
relatively strong. The CaII (H and K) lines are strong and very broad.
Finally, the presence of the HeI lines is seriously doubtful. The singlet lines
are absent while the triplet lines, present at lambda lambda 4471 and 4026,
must be identified (at least as major contributors) with the blend FeI (2),
TiI (146) and with TiI (12) respectively, whose multiplets are well represented
in the spectrum. The HeI at 3819 A, which Swings and Struve found "strong",
is absent. Therefore, the absorption spectrum shows well marked changes.
The emission spectrum of WY Gem consists of 12 forbidden lines, 11 of
[FeII] and 1 of [SII], compared with 6 observed by previous authors. The
identification of the lines and their estimated intensities are given in
Table IV. The radial velocities have been measured on two spectrograms
(dispersion 40 A/mm at Hgamma). The displacements of the lines of different
elements are listed in Table I.
It is interesting to note that all the lines, both M spectrum absorption
lines and forbidden emission lines, exhibit the same displacement. The
mean radial velocity of M spectrum absorption lines seems to be slightly
variable by considering the previous determinations: +18.2 km/s (Mt. Wilson)
and +10 +- 2 km/s (Redman, 1938).
W Cep (= HD 214369) was classified by Bidelman (1954) as VV Cep type
star. The available spectral classifications are: Harvard (HD): Kp; Mt.
Wilson: Mep; Bidelman (1954): K0epIa.
Table I
Radial velocities in WY Gem
Dec. 12, 1967 Mar. 12, 1968
(km/s) (km/s)
Selected lines of M spectrum (absorption) +26 +- 1 +33 +- 2
FeI " +29 +- 1 +34 +- 1
V I " +28 +- 1 +36 +- 3
CrI " +27 +- 2 +35 +- 3
TiI " +27 +- 1 +35 +- 3
CoI " +28 +- 3 +31 +- 3
MnI " +29 +- 4 +32 +- 3
Ionized metals " +29 +- 3 +31 +- 2
Balmer lines (Hbeta, Hgamma,
Hdelta) " +28 +- 4 +32 +- 4
Forbidden lines (emission) +27 +- 2 +30 +- 3
Mean +27 +- 1 +34 +- 2
W Cep was observed by Merrill et al. (1932). They found Halpha in
emission, variable in intensity. The only description of W Cep spectrum
is that of Swings and Struve (1940): the star was similar to WY Gem, though the
[FeII] emission lines were weaker than in WY Gem. Moreover, they found a
continuous spectrum extending far into the ultraviolet and "a strong,
but sharp, line at CaII K". At present, the late-type absorption
spectrum is that of a normal K3 supergiant with the continuous spectrum
very weak below 3900 A. As for WY Gem, the examined plates give no
evidence of HeI spectrum. In agreement with Swings and Struve's
observations, the [FeII] emission lines are weaker than in WY Gem. The
identification of the lines and their estimated intensities are given in
Table IV. Of greatest interest is the Balmer series structure: we find
Hbeta Hgamma, Hdelta with a weak sharp emission component displaced
toward the red by about 30 Km/s. Halpha is present strong in emission and
variable in intensity. Down from Hdelta the Balmer lines are in absorption.
The radial velocities have been measured on the best spectrogram
(dispersion 40 A/mm at Hgamma). The displacements of the lines of different
elements are listed in Table II.
Table II
Radial velocities in W Cep
Dec. 12, 1967
(km/s)
Selected lines of K spectrum (absorption) -39 +- 2
FeI " -37 +- 2
CrI " -40 +- 4
TiI " -40 +- 3
V I " -39 +- 3
Ionized metals " -37 +- 3
Forbidden lines (emission) -37 +- 2
Mean -38 +- 2
Fig. 1. Spectra of EG And.
The spectrum of HD 4174 (EG And) was described by Wilson (1950). He
found a gM2 background absorption spectrum and an emission spectrum
consisting of the Balmer series from Hbeta to H18 and of the three nebular
lines lambda lambda 3868 and 3967 of [NeIII] and 4363 of [OIII]. Babcock (1950)
found Hbeta variable "in intensity and character". Photometric and magnetic
variations have been found by Jarzebowski (1965).
Our plates (taken during the years 1966 to 1968) show very marked
variations mainly in the emission spectrum (Fig. 1).
In August 1966 Balmer emission lines (from Halpha to H11), and the
nebular lines of 4363 [OIII] and [NeIII] 3868 are present. Moreover, we
find in emission also CaII (K) at 3933A; the line is weak and superimposed
on a broad and diffuse absorption. All of the emission lines but [OIII] 4363
are narrow. In December 1966, [NeIII] 3868 becomes stronger. CaII K emission
line is absent while HeI 4026 appears in emission. In Jan 1967, that is in
less than one month, all the emission lines but OIII [4363] and [NeIII] 3868
disappear. In Dec. 1967, Halpha through H10 reappear in emission together
with [OIII] 4363, [NeIII] 3868, 3967, CaII (K) and two lines at lambda lambda
4243, 4248, identified as [FeII] (21F) and [FeII] (36F) respectively.
HeI 4026 is absent. In Aug. 1968, the hydrogen and CaII emissions lines
disappear while [OIII] 4363, [NeIII] 3868 and [FeII] 4243-4248 persist. The
estimated intensities give:
Aug. 10 Dec. 3 Jan. 4 Dec. 16 Aug. 19
1966 1966 1967 1967 1968
Hgamma : [OIII] 4363 2 3 - 4 -
[NeIII] 3868 : H8 0.7 2 - 1 -
[NeIII] 3868 : [NeIII] 3967 4 5 - 5 -
The radial velocities have been measured on the best spectrogram
(dispersion 40 A/mm at Hgamma). The displacements of the lines of
different elements are listed in Table III.
Table III
Radial velocities in HD 4174
Dec. 3, 1966
(km/s)
Selected lines of M spectrum (absorption) -104 +- 2
FeI " -102 +- 1
V I " 104 +- 2
MnI " -102 +- 4
CoI " -100 +- 4
TiI " -101 +- 3
CrI " -106 +- 4
CaI " -105 +- 4
Ionized metals " -101 +- 4
Forbidden lines (emission) -103 +- 4
Balmer lines (Hgamma, Hdelta,
Hepsilon, H8) " -101 +- 3
Mean -103 +- 3
Summarizing, we have found that: 1) the intensity variations previously
noted in HD 4174 are not confined to Hbeta. At least on two occasions (Jan 4,
1967 and August 19, 1968) all of the emissions, except [OIII] 4363,
[NeIII] 3868 and [FeII] 4243, 4249 disappeared. 2) No significant
differences between radial velocities inferred from absorptions and
emissions (both permitted and forbidden) have been revealed for the
three stars (the approaching velocity of HD 4174 is remarkably high). 3)
The shell lines noted by Swings and Struve in WY Gem are no longer
present, and the radial velocity is variable. We may be confronted with
a huge binary system, like VV Cep, Boss 1985 and Boss 5481, whose
late-type components are surrounded by extended atmospheres.
Table IV
Forbidden lines in the spectra of WY Gem, W Cep, HD 4174
Estimated intensities
lambda_0 Element WY Gem W Cep HD 4174
4457.95 FeII (6F) 3s - -
4452.11 FeII (7F) 4n - -
4416.27 FeII (6F) 3s - -
4413.78 FeII (7F) 3d 5b -
4402.60 FeII (36F) 3D 4D -
4363.21 OIII (2F) - - 5D
4359.34 FeII (7F) 5d - -
4319.62 FeII (21F) 3s 3s -
4287.91 FeII (7F) 8n 5n -
4276.83 FeII (21F) 3d 4D -
4249.07 FeII (36F) - 2d ?1s
4243.98 FeII (21F) 6D 7n ?2s
4231.56 FeII (21F) 2D 3d -
4178.95 FeII (23F) - 3s -
4068.62 SII (1F) 2s - -
3967.51 NeIII (1F) - - ?1s
3868.74 NeIII (1F) - - 5n
Notes: s = sharp; d = diffuse; D = very diffuse; n = narrow; b = broad
REFERENCES
Adams, W. S., Joy, A. H., Humason, M. L. and Brayton, A. M., 1935, Astrophys. J.
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Bidelman, W. P., 1954, Astrophys. J. Suppl. 1, 175.
Jarzebowski, T., 1965, I. A. U. Bamberg Coll. on Variable Stars.
Merrill, P. W., Humason, M. L. and Burwell, C. G., 1932, Astrophys. J. 76, 156.
Redman, R. O., 1938, Publ. Dom. Obs. Victoria 6, 27.
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