4.1. The orbital period and the distance to V1101 Aql
We can interpret the modulation in the V lightcurve of V1101 Aql as due to the orbital motion of the secondary star around the hot WD (see Warner 1995 and references therein). The UV illumination from the disk and the WD heats the inner face of the secondary and makes it brighter than the other side. This, combined with the orbital motion, produces a sinusoidal lightcurve with the maximum in correspondence of the superior conjunction of the secondary. The small amplitude of the modulation also indicates that eclipses are absent, and thus that the inclination of the system must be small.
The periodic variation of is consistent with the mean orbital period of Z Cam stars, which is always more than 3 hours (Warner 1995). DNe with these periods have early-mid M type secondaries (Ritter & Kolb 1995) with masses around 0.3-0.4 .
This orbital period determination can also lead us to attempt an estimate of the absolute magnitude of the system and hence its distance. According to Warner (1995), Z Cam DNe with orbital periods around should have (1 ) at standstill. If V1101 Aql has, at standstill, , (we assume the magnitude at quiescence to be ; see Pastukhova & Shugarov 1994) we derive, after taking into account the interstellar absorption in the V band, a distance of pc. This value is about one half the previous estimate given by Pastukhova & Shugarov (1994) and, together with the galactic latitude , implies a height on the galactic plane pc.
4.2. The spectrum and the nebulosity
The spectrum presented in Fig. 6 shows the presence of absorption Balmer lines filled in with emissions, thus supporting, in agreement with Pastukhova & Shugarov (1994), that this system might be a CV.
Concerning the asymmetric nebulosity around V1101 Aql, we note that it is more visible in V than in B (see Fig. 5a,b). Actually, simple aperture photometry gives and . The total angular size of the nebulosity is arcsecs; this, together with our distance estimate, leads to a linear size of cm.
© European Southern Observatory (ESO) 1998
Online publication: February 4, 1998