The Optical Transient Sky
Introduction:
In the first half of the twentieth century the search for and study of variable sources was a major focus of optical astronomy. This area is widely expected to undergo a renaissance, thanks to significant technological changes (sensors, computing, storage and dissemination). Apart from existing wide-field imagers dedicated facilities such as the Pan-STARRS and the LSST are motivated in part to explore transient phenomena in the optical sky.

A compilation of existing and planned survey telescopes can be found here.

In March 2006, we organized a two-day workshop discussing the status and future of the optical transient astronomy (Figure left). The Virtual Poster Session is available..
gsr1915


gsr1915 Flare Stars and Dwarf Novae:
A number of precursor surveys (e.g., DLS Transient Search, ROTSE-3) are already informing us of the difficulty of finding genuine new classes of transients. Solar system objects and flares from M dwarfs (Kulkarni & AR, 2006, ApJ, 644, L63) are now demonstrated to be the most common variable objects.

Another common contaminant are cataclysmic variables in their various incarnations. Especially dwarf novae (Figure left shows the light curve of ROTSE3 J160213.1-021311.7; AR et al., 2006, ApJ submitted), may cause a moderate foreground fog. Based on observations of dwarf novae superoutbursts we recently predicted that a few tens to a few hundred such sources can be expected in an all-sky snapshot.

Overcoming this fog will likely require dedicated surveys with careful optimization of target field location, filter(s), and cadence, presearch imaging to filter out late-type dwarfs, and a well-planned rapid follow-up plan. We are currently undergoing multiple such dedicated surveys at optical telesopes in the northern and southern hemispheres.


The Luminous Red Nova M85 OT2006-1
M85 OT2006-1 (Kulkarni, Ofek, AR, 2007, Nature, 447, 458 ) is the latest and most brilliant addition to the small group of known Luminous Red Novae (LRNe), which includes M31 RV, V432 Sgr & V838 Mon. These sources revelaed a large optical outburst lasting for a few weeks to months followed by a spectral red- ward evolution connected with an emerging infrared component.

Caltech Press Release

In a recent paper I reported the discovery of a similar feature in Keck/NIRC and Spitzer photometry of M85 OT2006-1 six months post-eruption (Figure right, AR et al., 2007, ApJ, 659, 1536). The infrared emission can be explained with optically thick dust emission of a black body with an effective temperature of approx. 1000K and a radius of approx 20000 solar radii. 		gsr1915


gsr1915 Transient Search at the ESO/MPG 2.2m:
One of the pre-precurors to Pan-STARRS and LSST was an optical survey performed using the Wide Field Imager at the 2.2m telescope at La Silla, Chile (Figure right). We monitored 12 square degrees in up to 25 nights typically spaced by two nights with a limiting magnitude of R=23 (AR et al., 2006, A&A, 449, 79).

The survey was originally designed to search for orphan afterglows. However, all four discovered previously unknown optical transients were found to be of known nature. We identified a flare star and a cataclysmic variable and used optical spectroscopy to reveal the nature of the remaining two as a second cataclymic variable and a solar system object (AR et al., 2006, ApJ, submitted).
last update : 2007-05-25
by: A. Rau - arne astro caltech edu
home