High Redshift Supernovae in the Hubble Deep Field

Two supernovae detected in the Hubble Deep Field using the original December 1995 epoch and data from a shorter (63000 s in F814W) December 1997 visit with HST are discussed. The supernovae (SNe) are both associated with distinct galaxies at redshifts of 0.95 (spectroscopic) from Cohen etal. (1996) and 1.32 (photometric) from the work of Fernandez-Soto, Lanzetta, and Yahil (1998). These redshifts are near, in the case of 0.95, and well beyond for 1.32 the greatest distance reported previously for SNe. We show that our observations are sensitive to SNe to z < 1.8 in either epoch for an event near peak brightness. Detailed simulations are discussed that quantify the level at which false events from our search phase would start to to arise, and the completeness of our search as a function of both SN brightness and host galaxy redshift. The number of Type Ia and Type II SNe expected as a function of redshift in the two HDF epochs are discussed in relation to several published predictions and our own detailed calculations. A mean detection frequency of one SN per epoch for the small HDF area is consistent with expectations from current theory.Comment: 62 pages, 17 figures, ApJ 1999 in pres

NICMOS Observations of the Transiting Hot Jupiter XO-1b

We refine the physical parameters of the transiting hot Jupiter planet XO-1b and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There are no significant differences in the XO-1 system properties between these broad-band NIR observations and previous determinations based upon ground-based optical observations. We measure two transit timings from these observations with 9 s and 15 s precision. As a residual to a linear ephemeris model, there is a 2.0 sigma timing difference between the two HST visits that are separated by 3 transit events (11.8 days). These two transit timings and additional timings from the literature are sufficient to rule out the presence of an Earth mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We identify and correct for poorly understood gain-like variations present in NICMOS time series data. This correction reduces the effective noise in time series photometry by a factor of two, for the case of XO-1.Comment: 13 pages, 8 figures, submitted to Ap

HST Fine Guidance Sensor Astrometric Parallaxes for Three Dwarf Novae: SS Aurigae, SS Cygni, and U Geminorum

We report astrometric parallaxes for three well known dwarf novae obtained using the Fine Guidance Sensors on the Hubble Space Telescope. We found a parallax for SS Aurigae of Pi = 5.00 +/- 0.64 mas, for SS Cygni we found Pi = 6.02 +/- 0.46 mas, and for U Geminorum we obtained Pi = 10.37 +/- 0.50 mas. These represent the first true trigonometric parallaxes of any dwarf novae. We briefly compare these results with previous distance estimates. This program demonstrates that with a very modest amount of HST observing time, the Fine Guidance Sensors can deliver parallaxes of unrivaled precision.Comment: 15 pages, 2 Table

Population Models with Diffusion and Constant Yield Harvesting

In this paper we discuss reaction-diffusion equations arising in population dynamics with constant yield harvesting in one dimension. We focus on the mathematical models of the logistic growth, the strong Allee effect, and the weak Allee effect and their influence on the existence of positive steady states as well as global bifurcation diagrams. We analyze the equations using the quadrature method and the method of sub-super solutions

Recovery of the old nova V840 Ophiuchi: A carbon rich system

We present optical spectroscopy and multi colour photometry of the old nova V840 Oph. We rediscovered the nova based on its position in the colour--colour diagrams. It stands out as a very blue object with an additional red component. We present the first optical spectroscopy of this candidate and confirm its nova character. Furthermore, V840\,Oph has been found as one of very few cataclysmic variables showing C IV emission at lambda = 580/1 nm. From the analysis of the carbon lines it seems probable that V840 Oph contains actually a carbon-rich secondary star. So far, only the nova-like QU Car has been known to have such a companion. We furthermore find spectroscopic evidence that V840 Oph has a hot, dense accretion disc or stream and is probably a magnetic system.Comment: 7 pages, 6 figures, accepted by A&