HST/STIS-enabled spectroscopic studies of the Ejecta of Eta Carinae: Clues to the Pseudo-Supernovae
Theodore Gull (NASA/GSFC)
The 1840s Great Eruption of Eta Carinae led to ejection of at least 15, possibly 40, solar masses in the form of a bipolar nebula with intervening skirt, known as the Homunculus. A lesser ejection in the 1890s led to the Little Homunculus, discovered by HST/STIS mappings. From the STIS FUV to the STIS NIR, multiple structures have been revealed and studied by STIS. In LOS, the UV high dispersions of STIS, combined with the diffraction-limited spatial resolution of HST, revealed over thirty velocity components, most within the -513 km/s shell of the Homunculus. Molecular hydrogen, NH, CH, and OH were identified. Eta Carinae is a massive binary with a 5.5-year period. During the spectroscopic high state (IP>13.6 eV) nearly a thousand molecular hydrogen lines are seen in LOS, but all disappear during the low state (IP<7.8 eV). For the first time, lines of SrII, VII, ScII (both in absorption and in nebular emission) were seen in nebular systems, plus lines of many other iron peak elements. The Strontium Filament, an ionized metal region (IP<7.8 eV) was discovered by HST/STIS leading to detailed studies of metal abundances providing important clues on the dust formed during the massive ejection. With the well-established 5.5 year binary period, Eta Carinae and the Homunculus are an astrophysical laboratory enabling atomic and molecular spectroscopic studies not possible in earth-based laboratories.
The HST/STIS spectroscopic data has contributed much both to atomic and molecular spectroscopy and to knowledge of how massive stars lose massive amounts of material in the Luminous Blue Variable stage. Very significant clues have been provided leading to increased knowledge of the pseudo-supernovae phenomenon seen in nearby galaxies: stellar brightenings that almost reach that of a supernova, but then slowly fade. In the example of SN2009ip, a near-supernova brightening occurred in 2009 and 2010 has now apparently reached a supernova state. Eta Carinae is expected to eventually evolve into one, possibly, two supernovae. By further studies of this rare, brief transitional state that Eta Carinae and the Homunculusis undergoing, we can gain much more insight on the evolution of massive stars in binary systems that may lead to phenomena like SN2009ip.
From Lyman Alpha to the Lyman Limit: Observing with COS in the Lyman UV (LUV)
Steven Penton (Space Telescope Science Institute)
New Cosmic Origins Spectrograph (COS) observing modes have extended the Hubble Space Telescope's spectral range to wavelengths between 900-1150┼. However, the G140L/1280 and the Cycle 19 available G130M central wavelengths (1055 and 1096) that sample below 1150┼ were only available at focus positions which provided low-resolution (R < 3,000). For HST Cycle 20, we introduced a new G130M/1222 central wavelength that covers 1065-1365┼ with R > 10,000 everywhere, but optimized for R~15000 from 1080-1200┼. This mode places geo-coronal Lyman-alpha between the COS FUV detector segments to minimize detector gain sag. Also for Cycle 20, the resolution of the G130M/1055 and 1096 modes have been
increased by a factor of 3-4 by optimizing the focus positions for these modes. This will give HST approximately the effective area of FUSE over the FUSE bandpass at R~10,000. Here we present the current calibration status of the COS G130M/1055, 1096, and 1222 central wavelength settings at the original and second FUV lifetime positions with an emphasis on observing over the "Lyman UV", or "LUV", 912-1216┼.
Model-Atmosphere Spectra for Hot, Compact Stars – Access via the Virtual Observatory Service TheoSSA
Thomas Rauch (IAAT, Eberhard Karls University TŘbingen)
The German Astrophysical Virtual Observatory (GAVO) provides the registered Virtual Observatory (VO) service TheoSSA (Theoretical Stellar Spectra Access). It is dedicated to the easy access of VO users to theoretical stellar spectral-energy distributions, calculated with any model-atmosphere code. In a pilot phase, TheoSSA is based on the well established TŘbingen NLTE Model-Atmosphere Package (TMAP) for hot, compact stars.