A week after discovery, we began a campaign of observations of this odd nova using the UW-Madison Pine Bluff Observatory (PBO) 0.91m telescope and the CCD spectropolarimeter. The spectropolarimeter has a wavelength coverage of 3170 to 10500 A with a spectral resolution of 6 A. Table 1 shows the dates and details of the observations. Sky conditions were not always photometric. The lightcurve (Fig. 1) indicates the visual magnitude of this nova when we observed it.
[NOTE: Figure captions are at the end of the document]
Obs. Local Julian Wavelength Exp. # Date Date Coverage (secs) =========================================== 1) 08/31/95 249960.69 6054-10442 6400 2) 09/01/95 249961.67 3169-10442 12800 3) 09/04/95 249964.71 3181-10442 12800 4) 09/15/95 249975.80 3178-10442 12800 5) 10/13/95 250003.67 3184-10442 12800 6) 11/05/95 250026.71 3169-10442 18800 7) 11/22/95 250043.57 3172-10442 19200 8) 12/08/95 250059.55 3172-10438 19200 9) 12/16/95 250067.50 3169-10442 19200 10) 12/21/95 250072.53 3169-10438 12000 11) 12/28/95 250079.61 3169-10442 12800 12) 12/29/95 250080.53 3169-10438 12800 13) 01/05/96 250087.56 3169-10438 11520
The early development of Nova Cas 1995 consisted of the gradual deepening of the Balmer jump, higher Balmer and Paschen lines going into absorption and the increase in the FWHM of H-alpha (Table 2). The Ca II triplet (8498, 8542, and 8662 A) increased in strength with time, after first becoming prominent on 9/15 (Fig. 3). On 11/5, the Fe II 42 and 49 multiplets appeared in absorption (Fig. 4) and reappeared in emission on 12/16. The Balmer jump was deepest on 12/16 (Fig. 5), which was during Nova Cas 1995's peak visual brightness. Also at this time we saw a dip around 4300 A which we believe to be due to overlapping absorption lines of Fe II.
The most dramatic change in the spectra occurred on 12/21 when the continuum no longer appeared stellar (Fig. 6). Other changes obvious in this spectrum were the first appearance of helium, namely, He I 5875 A which partially filled in the Na D line, the appearance of the Paschen lines up to P20 in emission (Fig. 3), and the first appearance of O I 7774A. The following observations (12/28/95, 12/29/95 and 1/5/96) are marked by nearly flat continua with emission Balmer and Paschen jumps, strong Fe II lines and lines of He I and O I (Fig. 7). However no nebular lines have yet been observed. In addition on 12/28/95 there was an large increase in the equivalent width of H-alpha (Table 2).
Table 2 Equivalent widths and FWHM for H-alpha # Date FWHM V EW =============================== 1 08/31/95 16.95 775 -74 2 09/01/95 20.61 942 -68 3 09/04/95 17.47 799 -62 4 09/15/95 17.17 785 -43 5 10/13/95 18.77 858 -33 6 11/05/95 19.40 887 -29 7 11/22/95 21.16 967 -12 8 12/08/95 24.59 1124 -26 9 12/16/95 25.65 1172 -21 10 12/21/95 36.98 1690 -47 11 12/28/95 32.15 1470 -328 12 12/29/95 32.65 1492 -379 13 01/05/96 30.49 1394 -592
As expected from the variation in the observed polarization, the intrinsic polarization varied. There were some trends, though. There were times when the observed polarization was due solely to the ISP. However, in over half of the observations, there was intrinsic polarization. The majority of these values clustered around P ~ 0.4% and PA ~ 150 degrees +/- 10 degrees. (Fig. 9). There were three episodes of intrinsic polarization: from 9/4 to 11/5; 12/8 and 12/16; 12/28 to 1/5. We see that even 10 days after discovery there was intrinsic polarization which implies structure in the ejecta. We also see that the intrinsic polarization tends to have the same position angle which in turn implies a common geometry which may imply a preferred plane of ejection.
1) There are changes in the optical depth
and temperature of the ejecta as shown
by the changes in the hydrogen lines,
continua, and polarization.
2) The ejecta showed an asymmetrical
geometry in the early stages of Nova
Cas's evolution, as shown by the
existence of intrinsic polarization.
3) There is a preferred orientation of the
ejecta as shown by the consistent
position angle of the intrinsic
polarization.
4) There was an ejection episode around
12/16 as inferred from the increase
in polarization, the increase in visual
brightness, and the increased width of
H-alpha in the observations following.
5) We see a line at 9997 A which may be
a Ly-alpha pumped line of Fe II
In the future, we hope to obtain polarimetry of field stars in the
vicinity of Nova Cas 1995 in order to better determine the ISP. Our
main conclusion, that there is intrinsic polarization and asymmetry in
the ejecta, will not change, but the values of the intrinsic
polarization and position angle may change with a better ISP estimate.
We will continue observing this odd nova for as long as possible.
FIGURE CAPTIONS
Figure 1:Visual lightcurve of Nova Cas 1995, courtesy of Stig
Linander and Bjorn Granslo
Figure 2:Spectrum obtained on 9/1. Flux units are ergs/s/cm2
throughout. Lines of H, Ca, Na, and Fe are marked.
Figure 3: Close-up of spectral region around the Ca II infrared
triplet, Paschen lines, and Fe II 9997A
Figure 4: Spectrum obtained on 11/5. Note Fe II 42,49 in
absorption and higher Balmer lines in absorption
Figure 5: Spectrum obtained on 12/16. Note extremely deep
Balmer jump, and the depression bluewards of 4300A
believed to be due to overlapping Fe II lines.
Figure 6: Spectrum obtained on 12/21. See text for details
Figure 7: Spectrum obtained on 12/29. Note Balmer and Paschen
jumps in emission. See text for further details.
Figure 8: Observed polarization on 12/29. Boxes from top to bottom
are flux, polarization, and position angle. Dashed line
marks H-alpha.
Figure 9: Nova Cas 12/29, after ISP removed. Boxes as in Figure 8.
Note decrease in polarization through H-alpha.