Instruments on large optical telescopes -- A case study

In the distant past, telescopes were known, first and foremost, for the sizes of their apertures. Advances in technology are now enabling astronomers to build extremely powerful instruments to the extent that instruments have now achieved importance comparable or even exceeding the usual importance accorded to the apertures of the telescopes. However, the cost of successive generations of instruments has risen at a rate noticeably above that of the rate of inflation. Here, given the vast sums of money now being expended on optical telescopes and their instrumentation, I argue that astronomers must undertake "cost-benefit" analysis for future planning. I use the scientific output of the first two decades of the W. M. Keck Observatory as a laboratory for this purpose. I find, in the absence of upgrades, that the time to reach peak paper production for an instrument is about six years. The prime lifetime of instruments (sans upgrades), as measured by citations returns, is about a decade. Well thought out and timely upgrades increase and sometimes even double the useful lifetime. I investigate how well instrument builders are rewarded. I find acknowledgements ranging from almost 100% to as low as 60%. Next, given the increasing cost of operating optical telescopes, the management of existing observatories continue to seek new partnerships. This naturally raises the question "What is the cost of a single night of telescope time". I provide a rational basis to compute this quantity. I then end the paper with some thoughts on the future of large ground-based optical telescopes, bearing in mind the explosion of synoptic precision photometric, astrometric and imaging surveys across the electromagnetic spectrum, the increasing cost of instrumentation and the rise of mega instruments.Comment: Revised from previous submission (typos fixed, table 6 was garbled). Submitted to PAS

The nature of the DLS fast transients

The discovery and study of highly transient sources, especially those which rise to high brightness and then fade to obscurity, has been a major part of modern astrophysics. Well known examples include supernovae and novae. A byproduct of the Deep Lens Survey was the discovery of three transients which varied on a timescale of less than an hour. All three had faint and red counterparts, the brightest of which was identified with an M star. However, the remaining two showed hints of an extragalactic origin, one had a spatially extended counterpart and the other appeared in projection on the outskirts of a bright elliptical galaxy. If these two sources were really of an extragalactic origin then the two events represent a new class of exotic explosive transients. We undertook spectroscopic observations with the Keck telescope and find the two counterparts are also late type Galactic dwarfs. Our main conclusion is that flares from M dwarfs constitute a dense foreground fog and dominate over any plausible class of extragalactic fast transients by at least two orders of magnitude. Overcoming this fog will likely require dedicated surveys with careful optimization of target field location, filter(s) and cadence, pre-search imaging to filter out late type dwarfs and a well planned rapid followup plan.Comment: 4 pages, 2 figures, ApJL in press, referee's comments implemente

From gamma-ray bursts to fast radio bursts

The field of gamma-ray burst astronomy arguably went through three decades of growing pains before reaching maturity. What development lessons can be learned for the adolescent field of fast radio burst astronomy

PTF 11kx: A Type Ia Supernova with a Symbiotic Nova Progenitor

There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi