ALBERT

Description: SS Cygni and HL Canis majoris were observed by IUE for three consecutive nights in November of 1992. During the first two nights, simultaneous photometric ground-based observations of SS Cyg were made at the Ball State University Observatory. Observations of SS Cyg and HL CMa were also obtained simultaneously with the 90-inch telescope at the Steward Observatory on the last two nights of the IUE run. These spectroscopic observations covered the wavelength range from 4100 to 5000 A, while the spectra taken with the short wavelength camera on IUE resulted in wavelength coverage from 1150 A to 1980 A. SS Cyg is a U Geminorum-type dwarf nova with an orbital period of 6.6 hr. Good simultaneous UV and optical orbital coverage was obtained for this system. HL CMa is a Z Camelopardalis-type dwarf nova with a mean outburst interval of 15 days. The American Association of Variable Star Observers (AAVSO) reports that this system was in outburst 4 days after the observing run. Therefore, HL CMa may have been in a preoutburst state during these observations. Optical spectra of HL CMa indicate a warm front passed through the outer disk four days before outburst, but no changes were seen in the UV spectra. Signs of a preoutburst state were observed to develop in SS Cyg, but no outburst occurred for another 30 days.

Description: Near infrared images are presented of the Herbig-Haro 110 jet centered at the molecular hydrogen lines. The ratio of these lines provides a preliminary diagnostic of molecular gas excitation, which is expected from low velocity shocks and turbulent processes. It is suggested that the morphological properties of the molecular hydrogen emission are consistent with that of a boundary layer.

Description: In this study, we explore the link between the physical properties of the outflow as determined from optical imaging and spectroscopy, and compare these results with those obtained from observations in the near infrared.

Description: We present a series of molecular hydrogen images of the Herbig-Haro 1-2 system in the 1-0 S(1) transition at 2.121 microns, with a spatial resolution of approximately 2 sec. The distribution of H2 is then compared with that of the excitation, given by the (S II) 6717+6731 to H-alpha line ratio. We find that most optical condensations in the HH 1-2 system, including the VLA 1 jet, have H2 counterparts. H2 emission is detected in most low excitation knots, as expected for low velocity shocks (50 km/s less than), but also in high excitation regions, like in HH 1F and HH 2A min. For these latter objects, the H2 emission could be due to the interaction of the preionizing flux, produced by 150-200 km/s shocks, with the surrounding interstellar matter, i.e., fluorescence. The lack fluorescent lines in the ultraviolet (UV), however, suggest a different mechanism. H2 is detected at the tip of the VLA 1 jet, where the knot morphology suggests the presence of a second bow shock. H2 is detected also SE of HH 2E and SW of HH 1F, in regions with known NH3 emission.

Description: When a massive star explodes as a supernova, substantial amounts of radioactive elements-primarily Ni-56, Ni-57 and Ti-44 are produced. After the initial from shock heating, the light emitted by the supernova is due to the decay of these elements. However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium. The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellan Cloud. From 1994 to 200l, the ejecta faded owing to radioactive decay of Ti-44 as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejects, enabling us to analyse the structure and chemistry of the vanished star.

Description: We present non-Local Thermodynamic Equilibrium (LTE) synthetic spectra for a time series of observations of SN 1993J obtained on 1993 March 30-31, April 7, April 13-15, and June 13 UT. The spectra are dominated by hydrogen Balmer lines; neutral helium lines, which have been nonthermally excited; and Fe II features. The density profile evolves from an extremely steep 'brick wall' structure with an equivalent power-law index of about 50 on March 30 to a more typical SN II profile with a power law index of about 10. The early spectra are well fitted by a solar composition of metals, although an enhanced abundance of helium is required in order to fit the neutral helium lines. By June 13, the photosphere has receded deep into the helium layer, although there appears to be a layer of hydrogen at higher velocity. The distance is estimated for each epoch. While consistent results are found for spectra obtained in the month of April, the spread in distances from March to June is quite large. Our value for April is mu = 28.0 +/- 0.3 mag, consistent with the recent Cepheid distance to the host galaxy M81. We also compare our results to other implementations of the expanding photosphere method.

Description: Due to its proximity, SN 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN 1987A obtained approximately 10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of H(alpha) to date, the first 3D maps for [Ca II] lambda lambda 7292, 7324 [O I] lambda lambda 6300, 6364, and Mg II lambda lambda 9218, 9244, as well as new maps for [Si I] + [Fe II] 1.644 micrometers and He I 2.058 micrometers. A comparison with previous observations shows that the [Si I] + [Fe II] flux and morphology have not changed significantly during the past ten years, providing evidence that this line is powered by Ti-44. The time evolution of H(alpha) shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north-south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, H and [Si I]+[Fe II] 1.644 micrometers, show substructures at the level of approximately 200-1000 km s(exp -1) and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.

Description: We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Supernova survey with Hubble (CLASH). Using the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope (HST), we have imaged 25 galaxy-cluster fields and parallel fields of non-cluster galaxies. We report a sample of 27 SNe discovered in the parallel fields. Of these SNe, approximately 13 are classified as SN Ia candidates, including four SN Ia candidates at redshifts z greater than 1.2.We measure volumetric SN Ia rates to redshift 1.8 and add the first upper limit on the SN Ia rate in the range z greater than 1.8 and less than 2.4. The results are consistent with the rates measured by the HST/ GOODS and Subaru Deep Field SN surveys.We model these results together with previous measurements at z less than 1 from the literature. The best-fitting SN Ia delay-time distribution (DTD; the distribution of times that elapse between a short burst of star formation and subsequent SN Ia explosions) is a power law with an index of 1.00 (+0.06(0.09))/(-0.06(0.10)) (statistical) (+0.12/0.08) (systematic), where the statistical uncertainty is a result of the 68% and 95% (in parentheses) statistical uncertainties reported for the various SN Ia rates (from this work and from the literature), and the systematic uncertainty reflects the range of possible cosmic star-formation histories. We also test DTD models produced by an assortment of published binary population synthesis (BPS) simulations. The shapes of all BPS double-degenerate DTDs are consistent with the volumetric SN Ia measurements, when the DTD models are scaled up by factors of 3-9. In contrast, all BPS single-degenerate DTDs are ruled out by the measurements at greater than 99% significance level.