J/ApJ/760/10 BV light curves of γ Cas (1997-2011) (Henry+, 2012)
Rotational and cyclical variability in γ Cassiopeiae.
II. Fifteen seasons.
Henry G.W., Smith M.A.
<Astrophys. J., 760, 10 (2012)>
=2012ApJ...760...10H 2012ApJ...760...10H
ADC_Keywords: Stars, Be ; Photometry, UBV
Keywords: circumstellar matter; stars: emission-line, Be;
stars: individual: gamma Cas
Abstract:
The B0.5 IVe star γ Cas is of great interest because it is the
prototype of a small group of classical Be stars having hard X-ray
emission of unknown origin. We discuss results from ongoing B and V
observations of the γ Cas star-disk system acquired with an
Automated Photometric Telescope during the observing seasons
1997-2011. In an earlier study, Smith, Henry, & Vishniac
(Cat. J/ApJ/647/1375) showed that light variations in γ Cas are
dominated by a series of comparatively prominent cycles with
amplitudes of 0.02-0.03mag and lengths of 2-3 months, superimposed on
a 1.21 day periodic signal some five times smaller, which they
attributed to rotation. The cycle lengths clustered around 70 days,
with a total range of 50-91 days. Changes in both cycle length and
amplitude were observed from year to year. These authors also found
the V-band cycles to be 30%-40% larger than the B-band cycles. In the
present study, we find continued evidence for these variability
patterns and for the bimodal distribution of the ΔB/ΔV
amplitude ratios in the long cycles. During the 2010 observing season,
γ Cas underwent a mass-loss event ("outburst"), as evidenced by
the brightening and reddening seen in our new photometry. This episode
coincided with a waning of the amplitude in the ongoing cycle. The Be
outburst ended the following year, and the light-curve amplitude
returned to pre-outburst levels. This behavior reinforces the
interpretation that cycles arise from a global disk instability. We
have determined a more precise value of the rotation period,
1.215811±0.000030 days, using the longer 15-season data set and
combining solutions from the V and B light curves. Remarkably, we also
find that both the amplitude and the asymmetry of the rotational
waveform changed over the years. We review arguments for this
modulation arising from transits of a surface magnetic disturbance.
Finally, to a limit of 5 mmag, we find no evidence for any photometric
variation corresponding to the γ Cas binary period, 203.55 days,
or to the first few harmonics.
Description:
Our optical continuum observations of γ Cas were acquired with
the T3 0.4m APT at Fairborn Observatory, located in the Patagonia
Mountains of southern Arizona. Full details concerning our γ Cas
observing program can be found in Robinson et al. (2002ApJ...575..435R 2002ApJ...575..435R)
and SHV (Smith et al. 2006, Cat. J/ApJ/647/1375). Briefly, the T3 APT
was programmed to observe γ Cas once every two hours on every
clear night throughout its observing season. All observations were
made in the standard Johnson B and V passbands.
SHV presented 3135 V and 3157 B observations covering the nine
observing seasons 1997-2005. In 1998 the filter was changed to
another, which has been used in the meantime. Here, we present data
from six more observing seasons 2006-2011, for a total of 4675 V and
4716 B observations. All 15 years of data (1997-2011) are listed in
Table 1.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
00 56 42.53 +60 43 00.3 γ Cas = HD 5394
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 38 4814 Photometric observations of γ Cas for
seasons 1997-2011
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See also:
J/A+A/540/A53 : γ Cas radial velocity curve (Smith+, 2012)
J/A+A/537/A59 : Radial velocities of gamma Cas (Nemravov+, 2012)
J/AJ/143/101 : Kepler B-star variables classification (McNamara+, 2012)
J/AZh/88/34 : Long-term (1984-2008) JHKLM phot. of stars (Shenavrin+, 2011)
J/ApJS/187/228 : Hα profiles of Be stars (Silaj+, 2010)
J/ApJ/654/527 : Interferometric obs. of northern Be stars (Gies+, 2007)
J/ApJ/647/1375 : BV light curves of γ Cas (Smith+, 2006)
J/PAZh/32/672 : Spectrophotometry of 77 variable stars (Ruban+, 2006)
J/A+A/378/861 : Spectroscopy of Be stars (Chauville+, 2001)
J/A+AS/129/289 : Long-term spectrophotometry of Be stars (Moujtahid+ 1998)
J/A+A/284/515 : Long-term periodic variability in gamma Cas (Telting+ 1994)
J/PASP/106/949 : Multicolor polarimetry of Be stars (McDavid, 1994)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d RJD [50718/55991] Reduced Julian Date; HJD-2400000
12- 17 F6.3 mag dBmag ?=99.999 Variable-Comparison (gam Cas-HD 6210)
differential magnitude in B (1)
19- 24 F6.3 mag dVmag ?=99.999 Variable-Comparison (gam Cas-HD 6210)
differential magnitude in V (1)
26- 31 F6.3 mag Bchk ?=99.999 Check-Comparison (HD 5395-HD 6210)
differential magnitude in B (1)
33- 38 F6.3 mag Vchk ?=99.999 Check-Comparison (HD 5395-HD 6210)
differential magnitude in V (1)
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Note (1): The '99.999' signifies that the differential magnitude was discarded
because its internal standard deviation exceeded 0.01mag.
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History:
From electronic version of the journal
References:
Smith et al. Paper I. 2006ApJ...647.1375S 2006ApJ...647.1375S Cat. J/ApJ/647/1375
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 17-Jul-2014