Other
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8483g&link_type=abstract
HST Proposal ID #8483
Other
Hst Proposal Id #8483
Scientific paper
In the past two years, observations of Eta Carina have revealed much new and very exciting information. Augusto Damineli noted a 5.5 year period in the visible and near infrared spectroscopy. Michael Corcoran and Bish Ishibashi noticed modulation of the x-ray fluxes with various periodicities around 90 days before and after the xray and radio minimum in December 1997. Observations, done in March 1998 under proposal 7302 {Davidson et al} from 1640A to 10400A using STIS in GXXXM mode and the 50x0.1 arcsecond slit, revealed much new information in the immediate regions of Eta Carina. The slit orientation was slightly off the major axis of the Homunculus, but passed through Weigelt components B and D. Bish Ishibashi and Ted Gull have reduced the data and provided it to various team members. Torgil Zethson has identified well over 90 percent of the emission lines in the March 1998 spectrum and finds most to be FeII emission lines. Based upon the past ground-based history of Eta Carina, we expected that FeIII and other high ionization states would return within the year. STIS GTO observations {Ted Gull, PI program 8036} characterized a bright internal emission nebula by turning the slit 90 degrees for visit 1 and studying the changes in spectrum as the FeIII lines appear by using visit 2 with the identical slit orientation from March 19, 1998. Data from the four visits of STIS to Eta Carinae between December 1997 and February 1999 demonstrate that the star has brightened by a factor of two during that interval and that the immediate nebulosity has tripled in surface brightness. Moreover a small circular nebular shell, seen in multiple [Fe II] lines has disappeared and the opacity in the 2000 to 3000A region obscuring the star has lifted considerable as the Fe II is converting to Fe III. Given the strong changes in the spectrum, we have chosen to use the six orbits in two visits. Visit 1 will be a precise repeat of the March 1998 and February 1999 observations, adjusted for the increasing brightness and compacted into two orbits of CVZ time. Visit 2 is designed to map the integral nebula in Hbeta and [FeII] lines at a fully sampled spacing of 0.1" with the 52x0.1 slit. The Homunculus will be mapped in H alpha and FeII lines at 0.2" spacing. Our primary objective is to get a three-dimensional snapshot of the nebulosities around Eta Carinae at one epoch as we are finding considerable changes even in times only a few months apart. At the end of these observations, a series of exposures are designed with Eta Carinae behind the F2 fiducial by a POS TARG maneuver. THIS IS NOT 52X0.2F1 We will not have complete information on the inner 0.8" region as the four orbits CVZ do not accomodate. An additional two orbits would be necessary as the dynamic range requires a number of very specific observations.
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