[vsnet-chat 378] Re: possible nova in Sco - on periodic variations

[Taichi Kato <tkato>]

(from vsnet-alert 986, Alon Retter)
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-alert/msg00986.html

> Since my thesis subject is young novae, let me add a few words.
> If this object is indeed a nova, and a very fast one, periodic
> variations may soon be detected. In Nova V838 Her 1991, it was
> discovered from about 3 weeks after the outburst (Leibowitz et al. 
> 1992, Ap. J. 385, L49). They interpreted the eclipse in this system 
> as an eclipse of the accretion disk by the secondary. 
> 
> Well, in this nova, we were lucky to have a very high inclination, 
> but even if the inclination is small, periodic variations can be 
> found shortly after the outburst.
> 
> Our preprint on Nova V1425 Aquilae 1995, which will be presented 
> in a poster in the Jackson workshop states that the orbital period 
> of this nova was detected about 3 months after maximum light. Who 
> knows, it might have been there long before. The amplitudes there
> are about 1%, so it's probably a low inclination system.
> 
> Periodic variations were also discovered in other young novae.
> In Nova V1974 Cyg 1992 (DeYoung & Schmidt 1994, Ap.J. 431, L47)
> and Nova V705 Cas 1993 (Retter & Leibowitz, 1995, IAUC 6234) 
> they were observed about 2 years after the eruption, however, again
> they might have been there before, and there were not so fast novae.
> 
> I think, that it is very interesting to follow periodic variations
> in young novae. See for example the photometric papers on V1974 Cyg
> (DeYoung & Schmidt 1994, Ap.J. 431, L47, Semeniuk et al. 1994, Acta
> Astro., 44, 277, Semeniuk et al. 1995, Acta Astro., 45, 365, Skillman 
> et. al., 1997, PASP, 109, 114 and Retter, Leibowitz & Ofek, 1997, MNRAS, 
> 286, 745). The case of Nova V1500 Cyg 1975, mentioned by Kato is another
> beautiful example.
> 
> Our hands are tied for this purpose, since we are at the north
> here at the Wise Observatory (dec=30), however for those of you
> interested in continuous photometry on this object, I suggest to use
> red filters, either for a reflection effect or for an eclipse of the
> accretion disk, which might be deeper in the red.
> 
> Good luck, and see you in Jackson!
> 
> Alon Retter
> Wise Obs.

   The case of V838 Her = Nova Her 1991 was extremely interesting.
I was prompted by its rapidness of decline to test any possible indication
of V1500 Cyg-type variation.  The nova instead proved to be an eclipsing one!
The first indication of deep eclipses were observed on 1991 April 22
(cf. IAUC 5262), which was 29 days after the optical maximum.
There were also some indication of shallow secondary minima (at phase 0.5)
on April 20 and 21, and some hint of a shallow primary eclipse on
April 14.  The observation on April 12 covered this phase, but was
inconclusive because of the heavy cloud interference.

   My 1991 August observations showed a very steep eclipse ingress and
egress, just as in detatched subdwarf binaries, indicating the eclipsed
source was very compact, probably indicating the contribution from the
accretion disk was negligible.

   Regarding eclipses in young novae, the fast nova V1668 Cyg presents
another interesting example.  While a 0.4271-day periodicity was observed
during decline, the nova was later found to be an eclipsing binary
of 0.1384 day (Kaluzny, MNRAS 245,547).  The observed period is close
to three times of Porb, but the relation between them is unknown.
I wonder what was the case during the nova decline of the well-observed
eclipsing nova DQ Her.

Regards,
Taichi Kato

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