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\IBVShead{4766}{6 September 1999}

\IBVStitle{Cyclic Variability of V1101 A\lowercase{ql}}

\IBVSauth{T.~Kato, D.~Nogami, H.~Baba}

\IBVSinsto{Dept.\ of Astronomy, Kyoto University, Kyoto 606-8502, Japan, e-mail: tkato@kusastro.kyoto-u.ac.jp}

\SIMBADobj{V1101 Aql}
\IBVStyp{ dwarf nova }
\IBVSkey{Dwarf novae - photometry}

\begintext

V1101 Aql, originally discovered as an irregular variable, has been
regarded as a Z Cam-type dwarf nova (Meinunger 1965; Vogt and Bateson 1982). Pastukhova and Shugarov (1994) dealed with the long-term behavior of this star, showing the presence of occasional fadings. Downes et al.\ (1995) presented low-resolution spectroscopy, which supported the cataclysmic nature of the star, but the possibility of being a Herbig Ae/Be star remained. Masetti and Della Valle (1998) obtained time-resolved CCD
photometry, which indicated possible orbital periods of 3.46 or 4.00~hr.

Our observations were done using a CCD camera (Thomson TH~7882, $576 \times 384$ pixels, on-chip $2 \times 2$ binning adopted) attached to the Cassegrain focus of the 60-cm reflector (focal ${\rm length} = 4.8$~m) at
Ouda Station, Kyoto University (Ohtani et al.\ 1992). An interference filter was used which had been designed to reproduce the Johnson $V$ band. The exposure time was 30--90~s, depending on the transparency of the sky. The frames were first corrected for standard de-biasing and flat fielding, and were then processed by a microcomputer-based automatic-aperture photometry package developed by one of the authors (TK){}. The relative $V$ magnitudes of the variable were determined against GSC 1618.977, whose magnitude was determined as $V=11.96$ using the local comparison stars
by Misselt (1996). The constancy of the comparison was confirmed using GSC 1618.1649 ($V=13.51$). The summary of observations is given
in Table 1.

\begin{table}
\begin{center}
\caption{CCD observation of V1101 Aql}
\begin{tabular}{ccccc}
\hline
JD start$^a$ & JD end$^a$ & mag$^b$ & error$^c$ & $N^d$ \\
\hline
50291.999 & 50292.003 & 2.360 & 0.032 & 4 \\
50293.115 & 50293.118 & 2.320 & 0.013 & 5 \\
50294.109 & 50294.112 & 2.462 & 0.018 & 5 \\
50295.053 & 50295.057 & 2.506 & 0.042 & 5 \\
50296.094 & 50296.098 & 2.281 & 0.019 & 5 \\
50301.109 & 50301.120 & 2.018 & 0.004 & 9 \\
50302.148 & 50302.172 & 2.140 & 0.005 & 20 \\
50303.133 & 50303.144 & 2.310 & 0.006 & 10 \\
50304.156 & 50304.159 & 2.449 & 0.014 & 5 \\
50305.176 & 50305.176 & 2.425 & 0.007 & 2 \\
50307.137 & 50307.140 & 2.423 & 0.007 & 5 \\
50313.077 & 50313.081 & 2.214 & 0.004 & 5 \\
50314.107 & 50314.110 & 1.915 & 0.006 & 5 \\
50316.089 & 50316.092 & 2.018 & 0.008 & 5 \\
50321.054 & 50321.054 & 2.557 & - & 1 \\
50331.949 & 50331.952 & 2.023 & 0.010 & 3 \\
50333.994 & 50333.995 & 2.331 & 0.008 & 2 \\
50334.960 & 50334.962 & 2.519 & 0.017 & 3 \\
50337.918 & 50337.920 & 2.307 & 0.023 & 3 \\
50340.965 & 50340.967 & 2.340 & 0.006 & 3 \\
50341.937 & 50341.938 & 2.270 & 0.005 & 3 \\
50342.949 & 50342.951 & 2.065 & 0.016 & 3 \\
50401.879 & 50401.881 & 2.408 & 0.023 & 3 \\
50403.872 & 50403.872 & 2.782 & - & 1 \\
50629.113 & 50629.114 & 2.015 & 0.004 & 3 \\
\hline
\end{tabular}

\normalsize
\begin{tabular}{l}
$^a$ ${\rm JD}-2400000$ \\
$^b$ Magnitude relative to GSC 1618.977 \\
$^c$ Standard error of nightly average \\
$^d$ Number of frames \\
\end{tabular}
\end{center}
\end{table}

\IBVSfig{10cm}{4766-f1.ps}{Light curve of V1101 Aql}

\vskip-11pt
The overall light curve is given in Figure~1. The light curve shows
the quasi-periodic cyclic variation with a period of $\sim$14~d, and an
amplitude of 0.7~mag. The coverage by Pastukhova and Shugarov (1994)
was not dense enough to clearly illustrate this modulation. Though the period of the modulation is close to that typical of Z Cam-type dwarf novae, the amplitude is rather small. The presence of short excursions to faint states (Pastukhova and Shugarov 1994) is also unusual for Z Cam-type dwarf novae. However, the light modulation is reminiscent of FY Vul, which bears spectroscopic similarity to V1101 Aql (Downes et al.\ 1995). There may be a previously unrecognized group of low-amplitude dwarf novae. The Herbig Ae/Be classification may better explain the presence of occasional fadings, and the possibly associated nebulosity (Masetti and Della Valle 1998), but 0.7-mag cyclic variation seems to be unusual for this class of objects. Another object exhibiting similar activities is FY Per, whose cyclic variations, with a typical period of 20--30~d, and a full amplitude of $\sim$1.2 mag have been recently established (Watanabe and Maehara 1999), and whose nature has been also discussed as either a cataclysmic variable or a Herbig Ae/Be star (Okazaki 1993). More observations are needed to clarify the nature of this intriguing object.

\bigskip

This work is partly supported by the Grant-in-Aid for Scientific Research
(10740095) of the Japanese Ministry of Education, Science, Culture, and
Sports.

\references

Downes, R., Hoard, H. W., Szkody, P., Wachter, S., 1995, {\it AJ}, {\bf 110}, 1824

Masetti, N., Della Valle, M., 1998, {\it Astron.\ Astrophys.}, {\bf 331}, 187

Meinunger, L., 1965, {\it Mitt.\ Ver\"and.\ Sterne}, {\bf 3}, 110

Misselt, K. A., 1996, {\it PASP}, {\bf 108}, 146

Ohtani, H., Uesugi, A., Tomita, Y., Yoshida, M., Kosugi, G., Noumaru, J., Araya, S., Ohta, K., 1992, {\it Memoirs of the Faculty of Science, Kyoto University, Series A of Physics, Astrophysics, Geophysics and Chemistry}, {\bf 38}, 167

Okazaki, A., 1993, {\it Astrophys.\ Space Sci.}, {\bf 210}, 227

Pastukhova, E. N., Shugarov, S. Y., 1994, {\it Perem.\ Zvezdy}, {\bf 23}, 233

Vogt, N., Bateson, F. M., 1982, {\it Astron.\ Astrophys.\ Suppl.}, {\bf 48}, 383

Watanabe, T., Maehara, H., 1999, {\it VSOLJ Variable Star Bulletin}, {\bf 35}, in press

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