PI: Guy Stringfellow, U. of Colorado, Guy.Stringfellow@colorado.edu
Address: Center for Astrophysics and Space Astronomy, 389 UCB, Boulder, CO 80309-0389 USA
Title: LBVs - Caught in the Act!
Abstract: Luminous Blue Variable (LBV) stars represent an extremely rare class of luminous massive stars with high mass loss rates that reside at the top of the HR diagram. There are only a dozen confirmed Galactic LBVs known, and another 10 residing in the LMC and SMC combined. There is now a firmly established link between some supernovae impostors undergoing LBV outbursts prior to their actually exploding as supernova, indicating that the LBV phase can be an end point for massive star evolution - a new paradigm in massive star evolution. The LBV population in the Galaxy and Magellanic Clouds provide a unique opportunity for study that has mostly been overlooked using modern instruments. LBVs undergo large-amplitude variability of 1-3 magnitudes with some having semi-long duration cycles on time scales of years between minimum and maximum brightness; S Dor type variability or eruptions, the cause of which is not fully understood. On occasion they also experience giant eruptions, like those observed for $eta$ Car and P Cyg, or the extragalactic SN impostors SN 2009ip and SN 2005gl. Past spectral studies of LBVs have been infrequent and restricted to a small range of wavelength, primarily $<$4900$ m AA$. Only two LBVs - AG Car and AFGL 2298 - have better spectral time coverage over critical phases, but even these remain incomplete. Clearly further spectral studies are needed for additional LBVs to determine their similarities and differences. Ongoing monitoring using Chiron on the SMARTS 1.5m, and the spectra obtained indicate several LBVs to be in new states never before seen for these stars, and undergoing spectral variability on time scales of weeks to months. Spectral changes provide insight into the physical changes (e.g., temperature, radius, mass loss rate, wind density) during these cycles, and their study should assist in revealing the underlying physical mechanism(s) driving the changes. This program seeks to follow the spectral and photometric morphology of LBVs.
Program Type: Standard/Galactic
Run 1 (2016A): CT-1.5m-SVC/CHIRON -- 30.6hrs
Run 2 (2016A): CT-1.3m/ANDI -- 9.6hrs
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