A few individual notes follow on the photometric behavior of the program symbiotic stars, to the aim of assisting the interested reader in planning an observing strategy. An inspiring reading would also be the collected history of symbiotic stars assembled by Kenyon (1986).
While calibrating the photometric comparison sequences for this paper we
have also collected data on the program symbiotic stars. These
data will be presented and discussed elsewhere together with similar
data for more than another 100 symbiotic stars observed from ESO and Asiago.
To the reader's benefit we report in this section mean B and B-Vvalues for 1999 from the
survey (hereafter indicated as
MHZ: Munari, Henden and Zwitter, in preparation).
Draco C-1. This carbon symbiotic star belongs to the Draco dwarf galaxy (Aaronson et al. 1982). Infrared photometry by Munari (1991a) proves C-1 to be at the tip of the Draco AGB with very blue IR colors for a carbon star, probably caused by the low metal content of the parent galaxy (Munari 1991b). No outburst has been so far recorded and the orbital period is unknown. BVI photometry by Munari (1991c) seems to support a variability of the carbon giant with a period of 55 days. If confirmed, this would be among the shortest period known for carbon pulsating variables (cf. Claussen et al. 1987). MHZ report B=18.6 and B-V=+1.5 mag. ALS 2. Its symbiotic nature has been discovered by Acker et al. (1988). MHZ lists B=16.2 and B-V=+1.9 mag. The orbital period, type of variability and presence of historical outburst are unknown.
FG Ser. After the 1988-1994 outburst when it rose to
B=10.4 and B-V=+1.1, it is now back toward the quiescent B=13.8and B-V=+2.0 mag values. MHZ list B=13.5 and B-V=+1.7 mag.
Munari et al. (1992b) discovered eclipses during the outburst phase (of
= 2.3 mag and 120 days between first and fourth contact). From three
consecutive mimina Munari et al. (1995) derived the following ephemeris
V443 Her. No outburst has ever been recorded from this
fairly bright symbiotic star. Its behavior in quiescence has been investigated by
Kolotilov et al. (1995) who found a lightcurve dominated by a reflection effect
= 0.4 and
= 0.1 mag
amplitude. The minima follow the ephemeris
K 3-9. Originally classified among the planetary nebulae, its symbiotic star nature has been discovered by Acker et al. (1983). According to Ivison & Seaquist (1995) K 3-9 is among the brightest symbiotic radio sources, and could harbor a Mira variable and a WD locked in a permanent outburst state. A thick dust cocoon should encircle the binary system, and a huge external ionized nebular material completely dominates the optical spectra. The photometric properties, history and orbital period are unknown. MHZ report B = 18.3 and B-V=+1.3.
MWC 960. This is a bright symbiotic star neglected by the observers. Munari et al. (1992a) report B = 13.6 and B-V=+1.5 and MHZ list B = 13.8 and B-V=+1.6. The photometric properties, history and orbital period are unknown.
AS 323. Another object originally classified as a planetary nebula which later turned out to be a symbiotic star (Sabbadin 1986; Acker et al. 1983). MHZ report B = 15.2 and B-V=+1.0. The photometric properties, history and orbital period are unknown.
FN Sgr. Another bright symbiotic star that has been
overlooked by most observers even though reports of large variability date
back to Ross (1926). Outbursts have been recorded in 1924-1926 and
1936-1941. The brightness in quiescence seems to vary by a large amplitude
2 mag) with possible periodicities between 1 and 3
years (cf. Kenyon 1986 and references therein). Amateur visual observations
over the last few years show a pattern reminiscent of an eclipsing binary
following the ephemeris (Munari et al., in preparation):
V919 Sgr. Another bright object ignored by observers. According to literature review and new observations by Ivison et al. (1993), V919 Sgr varies between B = 12 and 14.2 mag. Its cool giant is definitively variable in the infrared by at least = 0.7 mag. The announcement of an outburst was made in 1991, but it is not yet proven it actually occurred (see Ivison et al. 1993). MHZ report B = 14.2and B-V=+1.2. The past photometric history and orbital period are unknown.
CM Aql. Another relatively bright symbiotic star that has been overlooked by most observers. Its range of variability extend from B = 13.0 to B = 16.5. Outbursts have been reported for 1914, 1925, 1934, 1950. CM Aql also attracted some attention in late 1992 when from the usual V=13.2 it rose for a short period to mag. The orbital period is unknown. MHZ report B = 14.6 and B-V=+1.3.
V1413 Aql. The star erupted into a symbiotic nova in late
1981, and has not yet returned to quiescence conditions. According to
Munari (1992), V1413 Aql presented in quiescence
one of the largest known reflection effects (B varying between 16.5 and
14.0 mag). When the star erupted into outburst, deep eclipses appeared
perfectly in phase with the minima of the reflection effect according the
Ap 3-1. Another example of an object originally classified as a planetary nebula, and which later turned out to be a symbiotic star (Allen 1984). Its photometric properties are unknown. MHZ list B = 19.1 and B-V=+2.1.
ALS 1. Its symbiotic nature has been discovered by Acker et al. (1988), who report V = 14.8 mag. MHZ lists V = 13.5 and B-V=+1.4 mag. The photometric properties, history and orbital period are unknown.
V335 Vul. A symbiotic nature for this carbon star has been
suggested only recently (Munari et al. 1999a). The star colors are very
red, with MHZ giving V = 12.9 mag and B-V=+5.1 for quiescence.
Munari et al. (1999b) caught the star on the rising branch of an
apparent outburst, with V = 11.3 and B-V=+3.1 and a ten-fold increase
in the intensity of emission lines. The orbital period is unknown.
According to Dahlmark (1993) the carbon star is a Mira variable of
10.5 < V < 13.2 range, and maxima given by the ephemeris
QW Sge. Examining 438 archive blue plates covering the period 1960-1992, Kurockin (1993) has discovered two outbursts: one extending from July 1962 to March 1972 with B = 11.5 at maximum, the other from May 1982 to September 1989 with a much more complex lightcurve and a peak brightness B = 12.0. Outside outburst phases the star is since first observations in 1898 at . MHZ lists B = 13.2 and B-V=+0.81 mag. QW Sge has an optical companion 3.5 arcsec to the north, that Munari & Buson (1991) classified as an F0 V star with B = 13.59 and B-V=+0.45. Our photometry gives different values, B = 13.18 and B-V=+0.83, with a large scatter of 0.25 mag between three different measurements (compared to the few millimag for nearby stars of similar brightness). All this suggests that the optical companion is itself a variable star, and this complicates the interpretation of photometry made with moderate or short focus telescopes that are not able to separate QW Sge from the close optical companion (as it is the case for most of the archive photographic plates). It seems relevant to observe QW Sge with enough spatial resolution to avoid contamination from the nearby companion and to characterize the type and amplitude of variability of the latter. If the companion should turn out to be a moderate-amplitude variable and/or of a predictable type (like an eclipsing system), it would be possible to remove its contribution from the photographic photometry collected on QW Sge over the last century. No orbital period has been determined for QW Sge.
LT Del. A large reflection effect (
= 0.5 and
= 0.2 mag) following the
Hen 2-468. The photometric properties, history and orbital period are unknown. MHZ list B = 16.6 and B-V=+1.8 mag.
V407 Cyg. Discovered as Nova Cyg 1936, it was found by
Meinunger (1966) to harbor a Mira variable with one of the longest pulsation
period known and maxima following the ephemeris
V627 Cas. Originally classified among the T Tau pre-main sequence variables, its symbiotic star nature was discovered by Kolotilov (1988). Kolotilov et al. (1996) has summarized the optical and infrared photometric properties of V627 Cas. The cool component seems to be a M2 supergiant in a post-AGB phase, pulsating with a 466 day period. The hot component presents flickering activity superimposed onto several different types of variability, including a secular dimming by = 2.0 mag in 60 years. This is a peculiar type of symbiotic star which needs more effort to be better characterized from a photometric point of view. To null the effect of flickering, the star should be observed more times per night and over a few consecutive nights in all the bands.
StH 32. Its symbiotic star nature has been discovered by Downes & Keyes (1988). The photometric properties are unknown. MHZ list B = 14.2 and B-V=+1.4.
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