Photoelectric Photometry Newsletter

News About Program Stars (and Others)

In the previous issue of this newsletter, we introduced several new Be stars to the photoelectric program. We also mentioned that it is desirable (for quality control) to measure the check star as often as the variable star and tlte comparison star. David Williams pointed out that the AAVSP PEP reporting format allows for only 6ne check star observation, as compared with three of the variable and comparison. My advice? One good observation of the check star is probably adequate.

R.W. Jones, of Fish Hoek, South Africa, has begun to monitor some of the neglected small-amplitude red variables (SARV's) in the AAVSO photoelectric photometry program - especially those below the celestial equator. He has provided impressive light curves for the 1997 season. AK Hya varies by 0.6 magnitude; there appear to be two time scales (as in many SARV's), one about a month, and the other an order of magnitude longer. SW Vir varies by 1.6 magnitudes (!) on a time scale of four months. FH Vir varies by 0.5 magnitude on a time scale of two months, and possibly a longer time scale as well. EV Vir varies by 0.4 magnitude, also on time scale of two months but with slower variations superimposed. V533 Oph also varies by 0.4 magnitude, on a time scale of two months. Mr. Jones' observations demonstrate the effectiveness of "adopting" a small number of stars and monitoring them regularly. It will be interesting to see the results of two or three seasons of work.

EG And is a symbiotic star - a pair of stars of unlike type. in this case, we have an M2.4III red giant, and a white dwarf with a mass of 0.4 sun. The binary systeem shows minima whose ephemeris is JD(min) 2445380 + 481 E, where E is the cycle number. Pereira, in Astrophysics and Space Science 240, 1-11 (1996), describes ultraviolet observations of this star, which are used to infer the size of the gaseous emitting region around the white dwarf. The eclipse minima are clearly visible in the ultraviolet flux.

As mentioned in a previous issue of this newsletter, this star was discovered to be a multi-mode pulsator during a special "campaign" in 1996. We also checked out the suspected-variable comparison stars. You can safely use HR 5534 (comparison) and HR 5454 (check).

Mu Cephei is a red supergiant star - one of the most luminous in our galaxy. Brelstaff et al. have recently published a period analysis of this star in the Journal of the British Astronomical Association, 107, 135-140 (1997), using visual observations. They find periods of 850 and 4400 days. They suggest that the 730-day period given in the General Catalogue of Variable Stars, and a period of 920 days which has also been reported, are actually "alias" periods of the 850-day period.

In case any of you had wondered where CH Cyg had gone: the following is the abstract of a paper "Renewed Activity of CH Cyg", presented by Margarita Karovska, Janet Mattei, and Chris Carilli at the recent AAVSO Fall Meeting: "The AAVSO liaht curve of the nearest S-type symbiotic star, CH Cyg, showed an unprecedented drop in the V magnitude in 1996. This event bears striking resemblance to an earlier outburst phase of CH Cyg when, following extreme fading on the V magnitude in 1984, a multi-component jet was ejected. Since October 1996, we carried out multi-frequency monitoring of the radio brightness of this system, using the Very Large Array. We detected a significant increase in the radio flux since May 1997 which may be associated with a jet formation in the system."

CX Dra is one of the new Be stars on the program, referred to above. Phil Manker (Georgia Southwestern State University) has sent a light curve of the 1997 behaviour. The star shows small variations in its 6.696-day binary period, but the main variations occur as it forms an expanding equatorial disc of gas around its equator. These variations have an amplitude of up to 0.3 magnitude, and a time scale of about two months. In 1997, they have been almost continuous.

This is a famous Be/X-ray binary which has been observed both visually and photoelectrically by the AAVSO. When its expanding equatorial disc of gas forms, it is several tenths of a magnitude brighter than when it is "naked". Roche et al. (Astron. Astrophys. 322, 139-146 (1997)) report on the recent (1995) disc loss in the star. After brightening prior to 1995, the star subsequently faded as the disc dispersed.

Figure 2. Recent V light curve of the Be/X-ray binary X Per, taken from the-reference given above.

This star was included as a comparison star for CH Cyg in 1989, because it appeared that one of the existing comparison stars might be variable. A few weeks ago, Sergio Dallaporta, in Italy, reported that, on some nights, the star was variable by several tenths of a magnitude. He suggested that it was an EA-type eclipsing binary, with a period of about 2.466 days.

Initially, I was a bit skeptical, because it had not appeared to be variable, and its spectral type (FSV) does not suggest an intrinsic variable. But when I checked the Hipparcos catalogue, which had just arrived in my library, I was interested to find that Hipparcos had discovered it to be variable with a period of 2.47 days, with a range of 7.47 to 7.68 in the Hipparcos system.

Congratulations to Mr. Dailaporta for his independent discovery of the variability and the period!

This summer, I received a message and a short preprint about this star from my colleague Petr Ha=anec in the Czech Republic. HD 6226 is an early B type star which shows occasional brightenings in V, which are accompanied by small reddenings. The star may be an unrecognized Be star - a star which occasionally develops an expanding equatorial ring of gas which produces additional brightness. On the basis of long-te= ground-based photometry, and photometry from the Hipparcos satellite, Petr Harmanec and his colleagues proposed that the brightenings of the star might be periodic, with a period of 481 days. on this basis, a brightening might be expected around the end of November 1997.

Two AAVSO photoelectric observers - Ken Luedeke and Jim Wood - took on the task of monitoring the star, starting in the summer. The results are in: the star was approximately constant until the beginning of November when, over 20 days, it brightened and faded by 0.1-magnitude, just as it had done several times before. The observed brightening came a month or so after the predicted time, but this may indicate that the phenomenon is quasi-periodic, not strictly periodic.

A few weeks ago, I received a message from Chris Stephan, from Sebring FL, about a visual comparison star for XY Lyr. He suspected, from his visual observations, that the star varied from 6.5 to 6.9 Chuck Scovil, the AAVSO's chartmaster, had been consulted, and had identified the star as NSV 11271 in the New Catalogue of Suspected Variable Stars. It is also HR 7041 and HD 173383 - a sixth-magnitude K5 star, probably a giant.

I immediately went to the Hipparcos Catalogue, which I had recently received. On the basis of 110 photometric observations over 3.5 years (1989 to 1993), the star was completely constant! It is possible, of course, that the star was constant during the Hipparcos mission, but variable after, but it seems more likely to me that the visual scatter is observational. Chris' latest roun of visual observations continues to suggest variability of up to 0.3 magnitude.

This may therefore be a "wild goose chase" but .... if you wish to follow this up, you could measure NSV 11271 (next season), using the comp and check stars for R Lyr. They are HD 175740 (HR 7146) and HD 175884.