Photoelectric Photometry Newsletter

HIPPARCOS Observations of AAVSO PEP Stars

Almost all of the stars on the AAVSO photoelectric photometry program were observed by the HIPPARCOS satellite during its 3.5-year mission. One of the by-products of this astrometric satellite was extensive photometry (typically 100- 300 observations) over the mission. The HIPPARCOS team carried out period analysis of most of the stars, and classified the stars into (strictly) periodic, and unsolved. Another important grouping was the several hundred long-period variables which were observed visually by AAVSO observers in support of the HIPPARCOS mission.

Most of the AAVSO PEPP stars were "unsolved". That means that the stars were semi-regular at best. We already know, from over a decade of AAVSO PEP observations, that most of these stars are semi-regular or irregular, or that they vary on two or more timescales. In this case, they would have been classified as 77 unsolved" in the initial analysis. It will be interesting to carry out a more detailed analysis using both the AAVSO and HIPPARCOS data.

One useful by-product of this photometry is the discovery that several of the comparison and check -stars in the program are possibly microvariable. At some point, we will carry out an analysis, and possibly change the comparison stars. In almost all cases, however, one of the comparison stars is constant.

The following are the results, published in the HIPPARCOS catalogue. The quoted magnitudes are HIPPARCOS (Hp) magnitudes, which are close but not identical to V magnitudes.

T Cet. Unsolved; 5.17 - 5.83. There are variations on a time scale of several hundred days.
AG Cet. Unsolved; 6.73 - 6.96. Comparison star HR 88 has a period of 7.34 days and an amplitude of less than 0.04. It is now named BE Cet and, from its spectral type G3V and period, is probably a BY Draconis variable.
TV Psc. Unsolved; 4.85 - 5.25.
EG And. Unsolved; 7.19 - 7.36. There are variations on a time scale of several hundred days.
Z Eri. Unsolved; 6.25 - 6.71. Comparison star HR 857 is an unsolved microvariable with an amplitude less than 0.04. It is KlV, likely an RS CVn star, and is named EP Eri.
RR Eri. Unsolved; 6.74 - 7.11.
RZ Ari. Unsolved; 5.30 - 5.64. There are variations on a time scale of several hundred days.
Rho Per. Unsolved; 3.23 - 3.43.
X Per. Unsolved; 6.78 - 6.85.
CE Tau. Unsolved; 4.29 - 4.51. The comparison star HR 1816 may be microvariable with an amplitude less than 0.03. Its spectral type is MLIII, so it is probably a small-amplitude red variable. The check star HR 1780 is a microvariable with a spectral type of F8V, a period of 3.65 days, and an amplitude less than 0.04. It is now named V1119 Tau, and is probably an ellipsoidal variable.
Alpha Ori. Unsolved; 0.33 - 0.62. The characteristic variations on a time scale of a year are apparent.
SS Lep. Unsolved; 4.96 - 5.01.
Eta Gem. Variable with a period of 233-00 days, and a range of 3.20 - 3.43. The light curve is sparse. The comparison star HR 2169 is a microvariable with an amplitude less than 0.05. It's spectral type is K4III. Some K giants are microvariable, and it is not clear whether they are radial or non-radial pulsators, or some other type of variable.
IS Gem. Constant 7 in agreement with the previous results of the AAVSO photoelectric program.
V614 Mon. Unsolved; 7.18 - 7.45. The comparison star HR 2655 may be microvariable with an amplitude less than 0.04. It's spectral type is K3III; see comment on Eta Gem comparison star.
RU Cam. Variable with a period of 22.24 days and an amplitude of 0.20; see elsewhere in this Newsletter. There is considerable scatter, indicating that the variations are not strictly periodic.
EW CMa. Unsolved; 4.36 - 4.42. There was a slow increase and decrease in brightness over the 3.5 year mission.
VZ Cam. Unsolved; 4.82 - 4.96.
U Mon. Unsolved; 5.80 - 7.82. This is a well-known RV Tauri star. The check star HR 2867 may be microvariable with an amplitude less than 0.03. It's spectral type is K5III; see comment on Eta Gem comparison star.
AK Hya. Unsolved; 5.84 - 6.52. The comparison star is microvariable with an amplitude less than 0.05. It's spectral type is MLIII, so it is similar to many of the other small-amplitude red variables in this progam.
RS Cnc. Unsolved; 5.18 - 6.11. The comparison star HR 3621 may be microvariable with an amplitude less than 0.04.
IN Hya. Unsolved; 6.48 - 6.91.
VY UMa. Unsolved; 5.88 - 6.11. The "old" check star HR 4047 is a Delta Scuti star with a period of 0.16 day and an amplitude of 0.07. It is now named EN UMa.
VW UMa. Unsolved; 6.93 - 7.31. The comparison star HD 92880 is microvariable with an amplitude of 0.06.
TV UMa. Unsolved; 6.63 - 7.01. The comparison star HD 101978 is microvariable with an amplitude of 0.05.
GK Corn. Unsolved; 6.76 - 6.96.
FS Com. Unsolved; 5.32 - 5.61.
SW Vir. Variable with a period of 153.60 days and an amplitude of 0.65. The comparison star is microvariable with an amplitude of 0.06.
FH Vir. Unsolved; 6.97 - 7.23.
FP Vir. Unsolved; 6.55 - 7.06.
EV Vir. Unsolved; 6.64 - 7.03.
W Boo. Variable with a period of 35.33 days and an amplitude of 0.09. This star has had a very interesting history. It appears to have changed period from 25 days in the 1980's to 50 days in the 1990's. The period of 35 days has also been observed. Both the comparison star HR 5534 and the check star HD 130446 may be microvariable with amplitudes of up to 0.03 and 0.04, respectively.
Tau-4 Ser. Unsolved; 6.05 - 6.40.
ST Her. Unsolved; 6.45 - 7.15.
AT Dra. Unsolved; 5.27 - 5.45.
Alpha Sco. Unsolved; 0.91 - 1.07.
AZ Dra. Unsolved; 6.90 - 7.35. There are clear (but modulated) variations on a time scale of 400 days in the light curve.
VW Dra. Constant, in agreement with the previous results of the AAVSO photoelectric photometry program. The comparison star HD 156890 is mi- crovariable with an amplitude of 0.06. It's spectral type is FO, so it could be a Delta Scuti star.
V449 Sco. Not observed by Hipparcos.
V533 Oph. Unsolved; 6.90 - 7.37.
V441 Her. Variable with a period of 63.81 d,-.ys, and an amplitude of 0.17, and some scatter. This is a Cepheid-like variable.
V2048 (66) Oph. Unsolved; 4.61 - 4.78. The star showed three small 17 outbursts" over the 3.5 year mission.
d Ser. Constant, in agreement with previous results of the AAVSO photo- electric photometry program.
AC Her. Variable with a period of 75.30 days, and an amplitude of 1.07. This is a well-known RV Tauri star.
R Lyr. Unsolved; 3.82 - 4.13.
CH Cyg. Unsolved; 7.47 - 8.25. This is a well-known symbiotic star. The comparison star HD 183203 is microvariable with an amplitude of 0.06.
V973 Cyg. Unsolved; 6.26 - 6.56. The check star is possibly microvariable with an amplitude up to 0.04. It's spectral type is.MOIII, so it may be a small- amplitude red variable, like many of the stars in this program.
CSV 5011. Constant, in agreement with previous results of the AAVSO photoelectric photometry program. The comparison star HD 190397 is variable with an amplitude of 0.13.
EU Del. Variable with a period of 62.27 days and an amplitude of 0.45, with some scatter.
U Del. Unsolved; 6.00 - 6.83.
V832 Cyg. Unsolved microvariable; 4.70 - 4.74. The star declined slowly in brightness during the 3.5 year mission.
FZ Cep. Unsolved; 6.72 - 7.22. The light curve is quite complex.
V1070 C g. Unsolved; 6.31 - 6.73. The comparison star HD 203713 is microvariable with an amplitude of 0.05.
W Cyg. Variable with a period of 132-00 days and an amplitude of 0.85) and considerable scatter. The check star HR 8284 may be microvariable with an amplitude of 0.04.
AB Cyg. Unsolved; 7.58 - 8.09. There are variations on a time scale of several hundred days.
V1339 Cyg. Unsolved; 5.90 - 6.12. The check star HR 8284 may be microvariable with an amplitude of 0.04. It's spectral type is MLIII, so it may be a small-amplitude red variable, like many of the stars in this program. It is already a suspected variable (NSV 13834).
Mu Cep. Unsolved; 3.62 - 4.14.
HK Lac. Variable with a period of 24.41 days and an amplitude of 0.28.
DM Cep. Unsolved; 6.91 - 7.06.
CSV 8775. This star may be microvariable with an amplitude of up to 0.03.
EW Lac. Unsolved; 5.27 - 5.43.
V509 Cas. Unsolved; 5.18 - 5.29. There was a general decline of brightness during the 3.5 year mission, with variations on a time scale of 200-400 days superimposed.
SZ Psc. Variable with a period of 3.96579 days and an amplitude of 0.35.
Chi Aqr. Unsolved; 4.85 - 5.06.
Lambda And. Variable with a period of 54.33 days and an amplitude of 0.21. The comparison star HR 8964 may be microvariable with an amplitude of up to 0.04.
TX Psc. Unsolved; 4.86 - 5.09.
Rho Cas. Unsolved; 4.57 - 4.75. There are clear variations, however, on a time scale of several hundred days. The comparison star HR 9010 may be microvariable with an amplitude of up to 0.03.
XZ Psc. Unsolved; 5.61 - 5.81.