MMTF: The Maryland-Magellan Tunable Filter

This paper describes the Maryland-Magellan Tunable Filter (MMTF) on the Magellan-Baade 6.5-meter telescope. MMTF is based on a 150-mm clear aperture Fabry-Perot (FP) etalon that operates in low orders and provides transmission bandpass and central wavelength adjustable from ~5 to ~15 A and from ~5000 to over ~9200 A, respectively. It is installed in the Inamori Magellan Areal Camera and Spectrograph (IMACS) and delivers an image quality of ~0.5" over a field of view of 27' in diameter (monochromatic over ~10'). This versatile and easy-to-operate instrument has been used over the past three years for a wide variety of projects. This paper first reviews the basic principles of FP tunable filters, then provides a detailed description of the hardware and software associated with MMTF and the techniques developed to observe with this instrument and reduce the data. The main lessons learned in the course of the commissioning and implementation of MMTF are highlighted next, before concluding with a brief outlook on the future of MMTF and of similar facilities which are soon coming on line.Comment: 38 pages, 12 figures, 3 tables, now accepted for publication to the Astronomical Journa

Lack of Transit Timing Variations of OGLE-TR-111b: A re-analysis with six new epochs

We present six new transits of the exoplanet OGLE-TR-111b observed with the Magellan Telescopes in Chile between April 2008 and March 2009. We combine these new transits with five previously published transit epochs for this planet between 2005 and 2006 to extend the analysis of transit timing variations reported for this system. We derive a new planetary radius value of 1.019 +/- 0.026 R_J, which is intermediate to the previously reported radii of 1.067 +/- 0.054 R_J (Winn et al. 2007) and 0.922 +/- 0.057 R_J (Diaz et al. 2008). We also examine the transit timing variation and duration change claims of Diaz et al. (2008). Our analysis of all eleven transit epochs does not reveal any points with deviations larger than 2 sigma, and most points are well within 1 sigma. Although the transit duration nominally decreases over the four year span of the data, systematic errors in the photometry can account for this result. Therefore, there is no compelling evidence for either a timing or a duration variation in this system. Numerical integrations place an upper limit of about 1 M_E on the mass of a potential second planet in a 2:1 mean-motion resonance with OGLE-TR-111b.Comment: 28 pages, 7 tables, 6 figures. Accepted by Ap

The Old Host-Galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational Wave Source

We present an analysis of the host-galaxy environment of Swope Supernova Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a gravitational wave source, GW170817. SSS17a occurred 1.9 kpc (in projection; 10.2") from the nucleus of NGC 4993, an S0 galaxy at a distance of 40 Mpc. We present a Hubble Space Telescope (HST) pre-trigger image of NGC 4993, Magellan optical spectroscopy of the nucleus of NGC 4993 and the location of SSS17a, and broad-band UV through IR photometry of NGC 4993. The spectrum and broad-band spectral-energy distribution indicate that NGC 4993 has a stellar mass of log (M/M_solar) = 10.49^{+0.08}_{-0.20} and star formation rate of 0.003 M_solar/yr, and the progenitor system of SSS17a likely had an age of >2.8 Gyr. There is no counterpart at the position of SSS17a in the HST pre-trigger image, indicating that the progenitor system had an absolute magnitude M_V > -5.8 mag. We detect dust lanes extending out to almost the position of SSS17a and >100 likely globular clusters associated with NGC 4993. The offset of SSS17a is similar to many short gamma-ray burst offsets, and its progenitor system was likely bound to NGC 4993. The environment of SSS17a is consistent with an old progenitor system such as a binary neutron star system.Comment: ApJL in pres

Twenty-One New Light Curves of OGLE-TR-56b: New System Parameters and Limits on Timing Variations

Although OGLE-TR-56b was the second transiting exoplanet discovered, only one light curve, observed in 2006, has been published besides the discovery data. We present twenty-one light curves of nineteen different transits observed between July 2003 and July 2009 with the Magellan Telescopes and Gemini South. The combined analysis of the new light curves confirms a slightly inflated planetary radius relative to model predictions, with R_p = 1.378 +/- 0.090 R_J. However, the values found for the transit duration, semimajor axis, and inclination values differ significantly from the previous result, likely due to systematic errors. The new semimajor axis and inclination, a = 0.01942 +/- 0.00015 AU and i = 73.72 +/- 0.18 degrees, are smaller than previously reported, while the total duration, T_14 = 7931 +/- 38 s, is 18 minutes longer. The transit midtimes have errors from 23 s to several minutes, and no evidence is seen for transit midtime or duration variations. Similarly, no change is seen in the orbital period, implying a nominal stellar tidal decay factor of Q_* = 10^7, with a three-sigma lower limit of 10^5.7.Comment: 14 pages, 5 figures, accepted to Ap

Deep Photometry of GRB 041006 Afterglow: Hypernova Bump at Redshift z=0.716

We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data (t<4 days) joined with published GCN data indicates a steepening decay, approaching F_nu ~t^{-0.6} at early times (<<1 day) and F_nu ~t^{-1.3} at late times. The break at t_b=0.16+-0.04 days is the earliest reported jet break among all GRB afterglows. During our first night, we obtained 39 exposures spanning 2.15 hours from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After t~4 days, the decay slows considerably, and the light curve remains approximately flat at R~24 mag for a month before decaying by another magnitude to reach R~25 mag two months after the burst. This ``bump'' is well-fitted by a k-corrected light curve of SN1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SNe bumps, GRB 041006 stakes out new parameter space for GRB/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/SN bumps, we see a hint of a possible correlation between their peak luminosity and their ``stretch factor'', broadly similar to the well-studied Phillips relation for the type Ia supernovae.Comment: ApJ Letters, accepted. Additional material available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB041006

A Spitzer Study of Comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT)

We present infrared images and spectra of comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger program to observe comets inside of 5 AU from the sun with the Spitzer Space Telescope. The nucleus of comet 2P/Encke was observed at two vastly different phase angles (20 degrees and 63 degrees). Model fits to the spectral energy distributions of the nucleus suggest comet Encke's infrared beaming parameter derived from the near-Earth asteroid thermal model may have a phase angle dependence. The observed emission from comet Encke's dust coma is best-modeled using predominately amorphous carbon grains with a grain size distribution that peaks near 0.4 microns, and the silicate contribution by mass to the sub-micron dust coma is constrained to 31%. Comet 67P/Churyumov-Gerasimenko was observed with distinct coma emission in excess of a model nucleus at a heliocentric distance of 5.0 AU. The coma detection suggests that sublimation processes are still active or grains from recent activity remain near the nucleus. Comet C/2001 HT50 (LINEAR-NEAT) showed evidence for crystalline silicates in the spectrum obtained at 3.2 AU and we derive a silicate-to-carbon dust ratio of 0.6. The ratio is an order of magnitude lower than that derived for comets 9P/Tempel 1 during the Deep Impact encounter and C/1995 O1 (Hale-Bopp).Comment: Accepted for publication in the Astrophysical Journal 48 pages, 15 figures, 10 table

Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months

We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and supernova contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of a supernova. The early afterglow light curve also shows deviations from the typical power-law decay. A supernova spectrum is first detectable ~7 days after the burst and dominates the light after ~11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the supernova explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.Comment: 57 pages, 13 figures, accepted by ApJ, revised per referee's comments, includes full photometry table. Data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB030329 or through WWW at http://cfa-www.harvard.edu/cfa/oir/Research/GRB

H-alpha Spectral diversity of type II supernovae

We present a spectroscopic analysis of the H-alpha profiles of hydrogen-rich type II supernovae. A total of 52 type II supernovae having well sampled optical light curves and spectral sequences were analyzed. Concentrating on the H-alpha P-Cygni profile we measure its velocity from the FWHM of emission and the ratio of absorption to emission (a/e) at a common epoch at the start of the recombination phase, and search for correlations between these spectral parameters and photometric properties of the V-band light curves. Testing the strength of various correlations we find that a/e appears to be the dominant spectral parameter in terms of describing the diversity in our measured supernova properties. It is found that supernovae with smaller a/e have higher H-alpha velocities, more rapidly declining light curves from maximum, during the plateau and radioactive tail phase, are brighter at maximum light and have shorter optically thick phase durations. We discuss possible explanations of these results in terms of physical properties of type II supernovae, speculating that the most likely parameters which influence the morphologies of H-alpha profiles are the mass and density profile of the hydrogen envelope, together with additional emission components due to circumstellar interaction.Comment: Accepted for publication in ApJ letters. 9 pages, 3 figures, 2 table