HT Cam: Discovery of Short-Term Fluctuations on Rapid Fading
(Left: CCD image of HT Cam taken by Tovmassian. Right: Light curve on December
29 by G. Billings)
H. Itoh reported on December 29 that HT Cam (a ultra short-period CV;
also renowned for its infrequent very brief outbursts) experienced an
unprecedentedly bright outburst reaching 12.2mag (vsnet-campaign
1250, 1251,
vsnet-campaign-dn
2006). J. Kemp confirmed the outburst at 13.1mag on December 30,
which however indicated a rapid decline (vsnet-campaign-dn
2008). A. Oksanen also reported a rapid decline in late December 30
(vsnet-campaign
1256, vsnet-campaign-ip
67, 68,
vsnet-campaign-dn
2009,2010).
T. Kato reported strong modulations during the rapid fading (vsnet-campaign-dn
2011, vsnet-campaign-ip
69). There were 0.063 d periodicity, which is longer than the reported
orbital period, and ~8 min period which is close to the quiescence periodicity.
These modulations had the other possibility to be interpreted by QPOs
(vsnet-campaign-ip
70, 71,
vsnet-campaign-dn
2013, 2014).
The long-period wave (close to the orbital period) persisted until nearly
4 mag below the maximum. The best period determined from the available
observations is 0.064 d. The short-term modulations (IP pulses, or QPOs?)
were strong when the system was between 14 and 15. Later on, these modulations
became less prominent, although the corresponding signal persisted
(vsnet-campaign-ip
74, vsnet-campaign-dn
2018). Mean decline rate of HT Cam on Dec. 30 was 4.8 mag/d (vsnet-campaign-ip
75, vsnet-campaign-dn
2019).
During the decline phase, there was an indication of two different stages
of decline. The first part resembles that of a plateau portion of a dwarf
nova outburst, with a slower decline, low amplitude of orbital (or superhump)
signals, and low amplitude of the 8 min signal. The latter part, which
we have been mostly referring to, showed much more rapid decline, large
amplitudes of orbital (or superhump) and 8-min signals (vsnet-campaign-ip
77, vsnet-campaign-dn
2021).
The object almost returned to quiescence level and stopped fading on December
31 (vsnet-campaign-ip
72, vsnet-campaign-dn
2015). Both modulations seem to persist (vsnet-campaign-ip
78, vsnet-campaign-dn
2022, vsnet-campaign-ip
79, vsnet-campaign-dn
2024). T. Kato analyzed the post-outburst light curve and reported
that the 8-9 min modulations had a rather broad power spectrum, suggesting
that the modulations have a nature of quasi-periodic oscillations (QPOs)
(vsnet-campaign-ip
81, vsnet-campaign-dn
2025). After retaining a post-outburst plateau for three days, HT
Cam started fading again on January 3 (vsnet-campaign-dn
2029, vsnet-campaign-ip
82). On January 4, the dominating periodicity changed to be 0.041
d. The period is different from the orbital period or periods of
oscillations seen during and after the outburst (vsnet-campaign-dn
2036, vsnet-campaign-ip
83).
Other articles:
vsnet-campaign-ip
73, vsnet-campaign-dn
2016
Links:
Sequence presented by B. Skiff, see [vsnet-campaign
1252], (also see [vsnet-campaign-dn
2007], [vsnet-campaign
1254])
Finding chart provided by Tovmassian:
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/CVs/RXJ0757/rxj0757p63_fchart.jpg
[vsnet-campaign
1253]
Photometry by G. Billings:
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/CVs/RXJ0757/HTCam_29.gif
[vsnet-campaign
1257]
Pulse light curve:
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/CVs/RXK0757/pulse.gif
[vsnet-campaign-dn
2014]
HT Cam Data presented by G. Billings:
http://www.telusplanet.net/public/obs681/HTCmmc29.txt
http://www.telusplanet.net/public/obs681/HTCmmc29.gif
[vsnet-campaign-data
85] [vsnet-campaign-ip
76] [vsnet-campaign-dn
2020]
VSNET special page for this object:
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/DNe/htcam.html