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[vsnet-preprint 22] FT Cam preprint
FT Cam preprint
Dear Colleagues,
The following paper on FT Cam is accepted for publication as IBVS No. 5082.
The figure is placed at:
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/FT_Cam/
Regards,
Taichi Kato
============================================================================
\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\def\h{\hbox{$\!^{\rm h}$}}
\def\m{\hbox{$\!^{\rm m}$}}
\def\s{\hbox{$\!^{\rm s}$}}
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\begin{document}
\IBVShead{xxxx}{xx May 2001}
\IBVStitletl{FT Cam: Outburst Photometry and Proper Motion}
\IBVSauth{Taichi~Kato$^1$, Makoto~Uemura$^1$, Hitoshi~Yamaoka$^2$}
\vskip 5mm
\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan,
e-mail: tkato@kusastro.kyoto-u.ac.jp,\\
uemura@kusastro.kyoto-u.ac.jp}
\IBVSinst{Faculty of Science, Kyushu University, Fukuoka 810-8560, Japan,
e-mail: yamaoka@rc.kyushu-u.ac.jp}
\IBVSobj{FT Cam}
\IBVStyp{UG}
\IBVSkey{dwarf nova, photometry, astrometry}
\begintext
FT Cam (=Antipin Var64) is a dwarf nova discovered by Antipin (1999).
Antipin (1999) reported two outbursts on Moscow plates, indicating that
the outbursts are relatively rare. The next outburst was detected
by Pietz (1998) on 1998 September 23.91 UT at magnitude 14.7.
Visual observations by Kinnunen (1998) suggested the possible presence of
short-term variations. This outburst faded relatively quickly.
In spite of intensive monitoring by VSNET observers, no further outburst
had been detected until Schmeer (2000a) reported another one on 2000
February 27.166 UT at unfiltered CCD magnitude 14.4. A later announcement
by Pietz (2000) tells that the outburst started on February 26.8 UT,
at unfiltered CCD magnitude 13.85. Pietz (2000) reported that the
star was fainter than 15.5 on the previous night. The large observed
interval (521 d) between outbursts supports the low outburst frequency
reported by Antipin (1999). We started CCD time-resolved photometry
to test the presence of short-term variations.
\vskip 3mm
The CCD observations were done using an unfiltered ST-7 camera attached to
the Meade 25-cm Schmidt-Cassegrain telescope. The exposure time was 30 s.
The images were dark-subtracted, flat-fielded, and analyzed using the
Java$^{\rm TM}$-based aperture photometry package developed by one of the
authors (TK). The magnitudes were determined relative to GSC 4049.90,
whose Tycho-2 magnitude is $V=11.08\pm0.08$ and $B-V=+0.30\pm0.11$.
The constancy of the comparison star during the run was confirmed using
several anonymous fainter stars. We obtained 228 useful frames on
2000 February 27, covering 0.126 d. The light curve drawn from these data
is presented in Figure 1.
\IBVSfig{10cm}{fig1.ps}{Light curve of FT Cam. Each point represents
an average of 0.0025 d bin.}
\vskip 3mm
The light curve shows a rather monotonous decline at a rate of 0.82
mag d$^{-1}$. No apparent large-amplitude modulations nor periodic
waves were detected. The lack of apparent superhumps was also confirmed
by independent observations by Pietz (2000). The relatively rapid decline
was confirmed by G. Poyner who observed the star at mag 14.7 on 2000
February 28.810 UT. Schmeer (2000b) further reported that the star
had returned to quiescence on 2000 March 1.140 UT. These observations
suggests that all known (including Antipin's detections) outbursts
of FT Cam only last 2--3 d. Although the lack of apparent superhumps
may be suggestive of an SS Cyg-type star, it may be that we have only
observed normal outbursts of an SU UMa-type star. Further monitoring
for outbursts, and detailed observations during outbursts are strongly
encouraged.
\vskip 3mm
Astrometry of FT Cam from our outburst images has yielded the J2000.0
position of 03\h 21\m 14\fs 33, +61\deg 05\arcm 26\farcs 3 (based on 13
GSC-ACT stars). This value is pretty close to other reported astrometry
of 03\h 21\m 14\fs 33, +61\deg 05\arcm 26\farcs 0 (Antipin 1999) and
03\h 21\m 14\fs 35, +61\deg 05\arcm 26\farcs 1 (Schmeer 2000a),
but our result is considered as more accurate because we used the ICRS-based
astrometric grid, GSC-ACT. The corresponding USNO A2.0 star (on the
same astrometric grid) has end figures of 14\fs 415, 25\farcs 73, which
is 0\farcs 8 different from the current measurement. The comparison of
DSS 2 plate taken on 1993 December 11 with DSS 1 (epoch 1954.074) further
confirms the noticeable proper motion between them. The observed
proper motion 0\farcs 02 yr$^{-1}$ is relatively large among dwarf novae
(cf. Harrison et al. 2000; Thorstensen 1999). The observed proper
motion suggests that FT Cam is a relatively nearby object, likely located
within 1 kpc from us, corresponding to the maximum trangential velocity of
100 km s$^{-1}$ (for a discussion on velocity dispersions of cataclysmic
variables, see Harrison et al. 2000). The inferred conservative upper
limit $M_V=+4$ mag of the absolute magnitude in outburst is marginally
consistent with known absolute magnitudes of dwarf novae (Warner 1987).
However, many of observed maxima having been fainter than 14.5, the object
may be intrinsically fainter than usual dwarf novae. This possibility may
be strengthened by the low outburst frequency and shortness of outbursts,
which are relatively unusual for dwarf novae, but are more typical for
outbursts of intermediate polars (IPs). Since the accretion disks in IPs
are magnetically truncated, this may explain the low luminosity and short
duration of outbursts. The identification of FT Cam with a relatively
hard ROSAT source 1RXS J032114.1+610535 may be a further support for the
IP interpretation. Further observations in quiescence in order to search
for possible coherent oscillations are encouraged.
\vskip 3mm
The authors are grateful to VSNET members for providing crucial observations
covering years, and P. Schmeer for promptly and publicly notifying the
outburst.
Part of this work is supported by a Research Fellowship of the
Japan Society for the Promotion of Science for Young Scientists (MU).
\references
Antipin, S. V., 1999, IBVS No. 4673
Harrison, T. E., McNamura, B. J., Szkody, P., Gilliland, R. L.,
2000, AJ, 120, 2649
Kinnunen, T., 1998, {\it VSNET observations}, No. 15703 \\
(available from
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/obs15000/msg00703.html).
Pietz, J., 1998, {\it VSNET alert circulation}, No. 2218 \\
(available from
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/alert2000/msg00218.html).
Pietz, J., 2000, {\it VSNET observations}, No. 26574 \\
(available from
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/obs26000/msg00574.html).
Schmeer, P., 2000a, {\it VSNET alert circulation}, No. 4285 \\
(available from
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/alert4000/msg00285.html).
Schmeer, P., 2000b, {\it VSNET alert circulation}, No. 4307 \\
(available from
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/alert4000/msg00307.html).
Thorstensen, J. R., 1999, IBVS No. 4749
Warner, B., 1987, MNRAS, 227, 23
\end{document}
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