New Helium Dwarf Nova SN 1998di
New Helium Dwarf Nova SN 1998di
(CCD image by M. Schwartz)
Hi -
I knew that this would happen sooner or later, but SN1998di is a cataclysmic variable (CV) that comes from a dwarf star that has ignited due to material taken off an unseen companion. The only consolation is that they are more rare than supernovae.
So, let's erase this one from the record books and let the CVers take over. Statistically speaking, this is never supposed to happen. So this means that the odds of it happening to you are astronomical (so to speak).
Good hunting!!!
Mike
> S. Jha, P. Garnavich, P. Challis and R. Kirshner, Center for Astrophysics, > report that a spectrum of SN 1998di taken by P. Berlind on Aug 4.4 UT at > the Whipple Observatory 1.5-m telescope (+ FAST spectrograph) exhibits a > blue continuum with shallow absorption troughs shortward of 500 nm. The > object appears 4" east and 4" north of an anonymous galaxy with a > recession velocity of 10750 +/- 30 km/s. The shallow absorption features > have widths of approximately 3000 km/s (FWHM) and correspond to He I > absorption at zero radial velocity. The spectrum resembles that of CR Boo, > a hydrogen-deficient dwarf nova, near maximum (Patterson et al., 1997, > PASP, 109, 1100). We conclude that SN 1998di is a Galactic dwarf nova > discovered in outburst projected near the distant anonymous galaxy. -- Michael Schwartz, Director Tenagra Observatories, Ltd. http://www2.netcom.com/~pfactors/tenagra.html
(from CVC 167, also vsnet-alert 2000)
New cataclysmic variable in Draco =================================
We have been informed by Michael Schwartz, Cottage Grove, OR about his discovery of a new cataclysmic variable in Draco : "I am 'responsible' for finding supernova 1998di in an anonymous galaxy (see IAUC 6982, that was issued on August 3rd). However, spectral observations now reveal that this is not a supernova, but a galactic dwarf nova in outburst, projected near a distant anonymous galaxy".
Michael Schwartz kindly has sent us full details about the related spectrographic analysis by Jha, Garnavich, Challis and Kirshner (Center for Astrophysics), that likely will appear in an IAUC tomorrow. The spectrum of the new dwarf nova resembles that of the helium dwarf nova CR Boo near maximum (Patterson et al., 1997, PASP, 109, 1100).
The new object is located at RA = 19h24m38s.19, Decl = +59o41'46".7 (equinox 2000.0), which is about 0".6 east and 3".8 north of the nucleus of an anonymous galaxy. A picture of the new object is available at the following URL : http://www2.netcom.com/~pfactors/tenagra.html
Some photometric observations :
1998 Jul 22.46 UT, [19 (M. Schwartz, unfiltered CCD image);
Aug 02.48 UT, 16.8 (M. Schwartz, unfiltered CCD image);
We strongly recommend CCD observers to photometrically monitor this object.
Tonny Vanmunster
There are only THREE helium dwarf novae. CR Boo, V803 Cen and CP Eri. Schwarz's discovery of "SN1998di" adds a great new specimen to this unique subgroup of dwarf novae. Observations are highly encouarged, are we are happy to receive observations (e.g. to vsnet-obs or to myself, either from the CV or SN communities) and feed back new fidings. All of the known three helium dwarf novae show very short-term variation (orbital period tens of miniutes, outburst-like oscillations every sub-day to days, and superoutburst quasi-periodically repeating with a typical time-scale of tens of days. Continued observations by the same instrument, with which one may gain aditional possibility of catching a supernova than by watching field CVs, is highly encouraged. The USNO A1.0-based (V-equivalent) VSNET chart [vsnet-chart 66] is available at:
http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-chart/msg00066.html
(Original image by the discoverer: http://www2.netcom.com/~pfactors/tenagra.html)Regards,
vsnet-chart 67
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