Dust Streamers in the Virgo Galaxy M86 from Ram Pressure Stripping of its Companion VCC 882

The giant elliptical galaxy M86 in Virgo has a ~28 kpc long dust trail inside its optical halo that points toward the nucleated dwarf elliptical galaxy, VCC 882. The trail seems to be stripped material from the dwarf. Extinction measurements suggest that the ratio of the total gas mass in the trail to the blue luminosity of the dwarf is about unity, which is comparable to such ratios in dwarf irregular galaxies. The ram pressure experienced by the dwarf galaxy in the hot gaseous halo of M86 was comparable to the internal gravitational binding energy density of the presumed former gas disk in VCC 882. Published numerical models of this case are consistent with the overall trail-like morphology observed here. Three concentrations in the trail may be evidence for the predicted periodicity of the mass loss. The evaporation time of the trail is comparable to the trail age obtained from the relative speed of the galaxies and the trail length. Thus the trail could be continuously formed from stripped replenished gas if the VCC 882 orbit is bound. However, the high gas mass and the low expected replenishment rate suggest that this is only the first stripping event. Implications for the origin of nucleated dwarf ellipticals are briefly discussed.Comment: 22 pages, 7 figures, Astronomical Journal, August 2000, in pres

Observations of the Type II-P SN 1991G in NGC 4088

We present VRI photometry and optical spectra of SN 1991G in NGC 4088. The strong Hα P-Cygni feature observed in the early spectrum coupled with the shape of the light curve demonstrate that SN 1991G is of type II-P (plateau). SN 1991G's plateau, which lasts ~120 days, is longer than that of other well-observed SNe. We combine our photometry and spectroscopy to estimate the time of the explosion to be JD 2448280+/-3 (1991 January 23 UT), 26 days before our first photometric observation. The expansion velocity of the material at the photosphere, derived from absorption lines in our spectra, of 5590+/-340 km/s at 22 days after the explosion is slower than that observed for all the SNe II studied by Schmidt et al. (ApJ, 395,366(1992)] other than SN 1987A. We find that the bolometric luminosity of SN 1991G is lower than that of typical SNe II-P during both its plateau phase and exponential tail and find that SN 1991G ejected less ^56^Ni than most other type II-P SNe. Using the analytical models of SNe II-P by Popov [ApJ, 414,712 (1993)], we compare the explosion properties of SN 1991G to SN 1969L and SN 1992am. This comparison suggests that the explosion energy of SN 1991G was likely smaller than that of the others, and that there may be a correlation of explosion energy with the mass of ejected ^56^Ni