The star DQ Ser (l = 
; b = 
) is quoted in the 4th
ed. of General Catalogue of Variable Stars-GCVS4 (Kholopov et al.
1987) as a slow irregular variable (type L) presenting a brightness
variation from 13.9 to 16.0 mag. Our spectra show a late continuum with
emission lines of Balmer series, HeI (
5876, 6678,
7065), HeII 
4686, CIII-NIII 
4640-4650, [OIII]
(
4363, 4959, 5007), OI 
8446 and CaII triplet
(
8498, 8542, 8662). Lines of Paschen series in 8598
Å and 8751 Å, as well a large number of FeII lines are also seen
(Figs. 1 (click here)a, b, c, d). The continuum of the late-type star is
compatible with a type M3-M5 when compared with the spectra presented
in Jacoby et al. (1984), Schulte-Ladbeck (1988)
and Medina Tanco &
Steiner (1995). The presence of a late-type continuum with emission
lines of HI, [OIII] and HeII indicates DQ Ser as a symbiotic star.
The U-B and B-V colours presented by DQ Ser (Table 2) are somewhat
bluer than those expected from a M3-M5 giant without emission lines.
This is characteristic of symbiotic stars in which H
+ [OIII]
lines enhance the emission in the filter B while the Balmer jump in
emission, quite common in such variables, can affect the U-B colour
by a significant amount (Munari et al. 1992; Kenyon 1986). The V-I
index which is not strongly affected by emission lines is also
consistent with symbiotic M giants (Munari et al. 1992).
DQ Ser also shows a double and asymmetric profile in the H
line, whose peaks are centred in 6563.9 Å and in 6566.2 Å (see
inserted box in Fig. 1 (click here)b). Such H
profiles are quite common
among symbiotic stars (Van Winckel et al. 1993).
DT Ser (l = 
; b = 
) appears in the GCVS4 as a
probable irregular variable of type I, with a brightness variation in
the range 13.2-13.9 mag. Due to its spectral type G0 with lines of
[OIII] (
4959, 5007), Bond (1978) suggested a
classification as probable symbiotic.
Accurate measurements of DT Ser are difficult because of its close and
bright companion star. This star, about 5 arcsec from the variable, has
V magnitude of 12.8 and B-V of 0.76. Our spectra of this companion
show the Balmer series in absorption. Other absorption lines, including
the G band, are also present. DT Ser is 
2.6 mags fainter as
estimated from our UBVRI photometry (Table 2). The extracted spectrum
of the variable shows Balmer lines in emission as well as [OIII]
(
5007, 4959) and HeI 
5876. A weak emission of
HeII 
4686 is also present (Figs. 1 (click here)e, f). The continuum is
inconsistent with being a M or K giant as it does not display any band
associated with these spectral types. We suggest this star to be a
yellow symbiotic. We should, however, note that it is difficult to
assign a specific spectral type because of the light contamination from
bright G companion. This fact also makes the measurements of line
fluxes and line ratios not reliable; so we do not included them in
Table 3 (click here).
Figures 2 (click here)a and b show finding charts for these objects.
Acknowledgements
We would like to thank R. Baptista, F.J. Jablonski and G.R. Hickel for obtaining UBVRI photometry. We also thank the referee, R. Viotti, for his valuable comments and suggestions. D. Cieslinski and F. Elizalde thank for the support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), under contracts 140587/89-6 and 142589/92-6.