Microlens Parallax Measurements with a Warm Spitzer

Because Spitzer is an Earth-trailing orbit, losing about 0.1 AU/yr, it is excellently located to perform microlens parallax observations toward the Magellanic Clouds (LMC/SMC) and the Galactic bulge. These yield the so-called ``projected velocity'' of the lens, which can distinguish statistically among different populations. A few such measurements toward the LMC/SMC would reveal the nature of the lenses being detected in this direction (dark halo objects, or ordinary LMC/SMC stars). Cool Spitzer has already made one such measurement of a (rare) bright red-clump source, but warm (presumably less oversubscribed) Spitzer could devote the extra time required to obtain microlens parallaxes for the more common, but fainter, turnoff sources. Warm Spitzer could observe bulge microlenses for 38 days per year, which would permit up to 24 microlens parallaxes per year. This would yield interesting information on the disk mass function, particularly old brown dwarfs, which at present are inaccessible by other techniques. Target-of-Opportunity (TOO) observations should be divided into RTOO/DTOO, i.e., ``regular'' and ``disruptive'' TOOs, as pioneered by the Space Interferometry Mission (SIM). LMC/SMC parallax measurements would be DTOO, but bulge measurements would be RTOO, i.e., they could be scheduled in advance, without knowing exactly which star was to be observed.Comment: 6 pages + 1 Figure, To be presented at The Warm Spitzer Mission Workshop, 4-5 June 2007, Pasaden

Spitzer Warm Mission Workshop Introduction

The Spitzer Warm Mission Workshop was held June 4–5, 2007, to explore the science drivers for the warm Spitzer mission and help the Spitzer Science Center develop a new science operations philosophy. We must continue to maximize the science return with the reduced resources available, both using (a) the shortest two IRAC channels, and (b) archival research with the rich Spitzer archive. This paper summarizes the overview slides presented to the workshop participant

The Warm Spitzer Mission: Prospects for Studies of the Distant Universe

IRAC excels at detecting distant objects. Due to a combination of the shapes of the spectral energy distributions of galaxies and the low background achieved from space, IRAC reaches greater depth in comparable exposure time at 3.6 and 4.5 micron than any ground- or space-based facility currently can at 2.2 micron. Furthermore, the longer wavelengths probed by IRAC enable studies of the rest-frame optical and near-infrared light of galaxies and AGN to much higher redshift than is possible from the ground. This white paper explores the merits of different survey strategies for studying the distant universe during the warm mission. A three-tiered approach serves a wide range of science goals and uses the spacecraft effectively: 1) an ultra-deep survey of ~0.04 square degrees to a depth of ~250 hrs (in conjunction with an HST/WFC3 program), to study the Universe at 7<z<14; 2) a survey of ~2 square degrees to the GOODS depth of 20 hrs, to identify luminous galaxies at z>6 and characterize the relation between the build-up of dark matter halos and their constituent galaxies at 2<z<6, and 3) a 500 square degree survey to the SWIRE depth of 120 s, to systematically study large scale structure at 1<z<2 and characterize high redshift AGN. One or more of these programs could conceivably be implemented by the SSC, following the example of the Hubble Deep Field campaigns. As priorities in this field continuously shift it is also crucial that a fraction of the exposure time remains unassigned, thus enabling science that will reflect the frontiers of 2010 and beyond rather than those of 2007.Comment: White paper to appear in "The Science Opportunities for the Warm Spitzer Mission". 15 page

Observations of Extrasolar Planets During the non-Cryogenic Spitzer Space Telescope Mission

Precision infrared photometry from Spitzer has enabled the first direct studies of light from extrasolar planets, via observations at secondary eclipse in transiting systems. Current Spitzer results include the first longitudinal temperature map of an extrasolar planet, and the first spectra of their atmospheres. Spitzer has also measured a temperature and precise radius for the first transiting Neptune-sized exoplanet, and is beginning to make precise transit timing measurements to infer the existence of unseen low mass planets. The lack of stellar limb darkening in the infrared facilitates precise radius and transit timing measurements of transiting planets. Warm Spitzer will be capable of a precise radius measurement for Earth-sized planets transiting nearby M-dwarfs, thereby constraining their bulk composition. It will continue to measure thermal emission at secondary eclipse for transiting hot Jupiters, and be able to distinguish between planets having broad band emission versus absorption spectra. It will also be able to measure the orbital phase variation of thermal emission for close-in planets, even non-transiting planets, and these measurements will be of special interest for planets in eccentric orbits. Warm Spitzer will be a significant complement to Kepler, particularly as regards transit timing in the Kepler field. In addition to studying close-in planets, Warm Spitzer will have significant application in sensitive imaging searches for young planets at relatively large angular separations from their parent stars.Comment: 12 pages, 7 figures, to appear in "Science Opportunities for the Warm Spitzer Mission

The Porcupine Survey: A Distributed Survey and WISE Followup

Spitzer post-cryogen observations to perform a moderate depth survey distributed around the sky are proposed. Field centers are chosen to be WISE brown dwarf candidates, which will typically be 160 µJy at 4.7 µm and randomly distributed around the sky. The Spitzer observations will give much higher sensitivity, higher angular resolution, and a time baseline to measure both proper motions and possibly parallaxes. The distance and velocity data obtained on the WISE brown dwarf candidates will greatly improve our knowledge of the mass and age distribution of brown dwarfs. The outer parts of the Spitzer fields surrounding the WISE positions will provide a deep survey in many narrow fields of view distributed around the sky, and the volume of this survey will contain many more distant brown dwarfs, and many extragalactic objects

Photometric Recovery of Crowded Stellar Fields Observed with HST/WFPC2 and the Effects of Confusion Noise on the Extragalactic Distance Scale

We explore the limits of photometric reductions of crowded stellar fields observed with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. Two photometric procedures, based on the DoPHOT and DAOPHOT/ALLFRAME programs are tested, and the effects of crowding, complex sky background and cosmic-ray contamination are discussed using an extensive set of artificial star simulations. As a specific application of the results presented in this paper, we assess the magnitude of photometric biases on programs aimed at finding Cepheids and determining distances. We find that while the photometry in individual images can be biased too bright by up to 0.2 mag in the most crowded fields due to confusion noise, the effects on distance measurements based on Cepheid variables are insignificant, less than 0.02 mag (1% in distance) even in the most problematic cases. This result, which is at odds with claims recently surfaced in the literature, is due to the strict criteria applied in the selection of the variable stars, and the photometric cross checks made possible by the availability of multiple exposures in different filters which characterizes Cepheid observations.Comment: Accepted for publication in PASP. 41 pages, 18 figures, 8 tables. The figures included with this submission are very low quality bitmap postscript, please see http://www.astro.ucla.edu/~laura/pub.htm for the full size image

SPRITE: the Spitzer proposal review website

The Spitzer Science Center (SSC), located on the campus of the California Institute of Technology, supports the science operations of NASA's infrared Spitzer Space Telescope. The SSC issues an annual Call for Proposals inviting investigators worldwide to submit Spitzer Space Telescope proposals. The Spitzer Proposal Review Website (SPRITE) is a MySQL/PHP web database application designed to support the SSC proposal review process. Review panel members use the software to view, grade, and write comments about the proposals, and SSC support team members monitor the grading and ranking process and ultimately generate a ranked list of all the proposals. The software is also used to generate, edit, and email award letters to the proposers. This work was performed at the California Institute of Technology under contract to the National Aeronautics and Space Administration

The Mid-Infrared Spectra of Normal Galaxies

The mid-infrared spectra (2.5 to 5 and 5.7 to 11.6 mu) obtained by ISO-PHOT reveal the interstellar medium emission from galaxies powered by star formation to be strongly dominated by the aromatic features at 6.2, 7.7, 8.6 and 11.3 mu. Additional emission appears in-between the features, and an underlying continuum is clearly evident at 3-5 mu. This continuum would contribute about a third of the luminosity in the 3 to 13 mu range. The features together carry 5 to 30% of the 40-to-120 mu `FIR' luminosity. The relative fluxes in individual features depend very weakly on galaxy parameters such as the far-infrared colors, direct evidence that the emitting particles are not in thermal equilibrium. The dip at 10 mu is unlikely to result from silicate absorption, since its shape is invariant among galaxies. The continuum component has a f_nu \~ nu^{0.65} shape between 3 and 5 mu and carries 1 to 4% of the FIR luminosity; its extrapolation to longer wavelengths falls well below the spectrum in the 6 to 12 mu range. This continuum component is almost certainly of non-stellar origin, and is probably due to fluctuating grains without aromatic features. The spectra reported here typify the integrated emission from the interstellar medium of the majority of star-forming galaxies, and could thus be used to obtain redshifts of highly extincted galaxies up to z=3 with SIRTF.Comment: 10 pages, 2 figures, uses AAS LaTeX; to appear in the Astrophysical Journal Letter