Photometry of Outer-belt Objects

We present results from multi-wavelength observations of outer-belt asteroid 279 Thule and comet C12002 CE10 (LINEAR). The orbital elements of the second object, formerly classified as asteroid 2002 CE10, at first led to its identification with a group of asteroids called the Damocloids. The Damocloids\u27 orbits are similar to Halley family comets (HFCs), and there is suspicion that the Damocloids are inactive HFC nuclei. Following observations by the 8.2 m Japanese Subaru telescope in August 2003, which determined that 2002 CE IO had a characteristic tail (Takato et al; 2003), it was re-classified as comet C/2002 CE10 (LINEAR). We observed these and other objects with filters close to the Johnson-Kron-Cousins BVRl filters corresponding to the blue, visible, red, and near-IR wavelengths using the 0.9m SMARTS telescope at Cerro-Tololo Inter-American Observatory during October 2003. Using the image reduction routines (imred) of the Image Reduction and Analysis Facility (NOAO Xl IIIRAF), we removed the bias caused by dark currents, and flat fielded the data to improve the signal-to-noise ratio (SNR). Instrumental magnitudes for all objects were extracted using the aperture photometry package (apphot). Landolt standard stars were used to solve the transformation equations and extract extinction coefficients. Photometric calibration routines (photcaI) allowed us to use the extinction coefficients and instrumental magnitudes to determine magnitudes in the Landolt standard system. We computed absolute magnitudes for 279 Thule and C/2002 CE10 (LINEAR) in the VR bands by correcting for the changing geocentric distance, heliocentric distance, and solar phase of the object. 279 Thule was found to have a mean absolute visual magnitude of 8.66±0.OJ and a V-R color of 0.44±0.03, when corrected for solar phase using the standard IAU phase relation (Bowell et al; J989). We discuss the suitability of the standard phase relation for 279 Thule. We place constraints on the size of the objects. We determine the rotation period for 279 Thule to be 7.6±0.5 hrs, using an implementation of the phase dispersion minimization (PDM) algorithm first developed by Stellingwerf (1978). It is likely that observations of C12002 CE lU (LINEAR) have been contaminated by near nucleus coma

The Changing Fractions of Type Ia Supernova NUV-Optical Subclasses with Redshift

UV and optical photometry of Type Ia supernovae (SNe Ia) at low redshift have revealed the existence of two distinct color groups, NUV-red and NUV-blue events. The color curves differ primarily by an offset, with the NUV-blue u- color curves bluer than the NUV-red curves by 0.4 mag. For a sample of 23 low-z SNe~Ia observed with Swift, the NUV-red group dominates by a ratio of 2:1. We compare rest-frame UV/optical spectrophotometry of intermediate and high-z SNe Ia with UVOT photometry and HST spectrophotometry of low-z SNe Ia, finding that the same two color groups exist at higher-z, but with the NUV-blue events as the dominant group. Within each red/blue group, we do not detect any offset in color for different redshifts, providing insight into how SN~Ia UV emission evolves with redshift. Through spectral comparisons of SNe~Ia with similar peak widths and phase, we explore the wavelength range that produces the UV/OPT color differences. We show that the ejecta velocity of NUV-red SNe is larger than that of NUV-blue objects by roughly 12% on average. This velocity difference can explain some of the UV/optical color difference, but differences in the strengths of spectral features seen in meanspectra require additional explanation. Because of the different b-v colors for these groups, NUV-red SNe will have their extinction underestimated using common techniques. This, in turn, leads to under-estimation of the optical luminosity of the NUV-blue SNe~Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.Comment: submitted to Ap

Light Curves of Type Ia Supernovae and Preliminary Cosmological Constraints from the ESSENCE Survey

The ESSENCE survey discovered 213 type Ia supernovae at redshifts 0.10 < z < 0.81 between 2002 and 2008. We present their R and I band light curve measurements, obtained using the MOSAIC II imager at the CTIO 4 m, along with rapid response spectroscopy for each object from a range of large aperture ground based telescopes. We detail our program to obtain quantitative classifications and precise redshifts from our spectroscopic follow-up of each object. We describe our efforts to improve the precision of the calibration of the CTIO 4 m natural photometric system. We use several empirical metrics to measure our internal photometric consistency and our absolute calibration of the survey. We assess the effect of various sources of systematic error on our measured fluxes, and estimate that the total systematic error budget from the photometric calibration is ~1%. We combine 108 ESSENCE SNIa that pass stringent quality cuts with a compilation of 441 SNIa from 3 year results presented by the Supernova Legacy Survey and Baryon Acoustic Oscillation measurements from the Sloan Digital Sky Survey to produce preliminary cosmological constraints employing the SNIa . This constitutes the largest sample of well-calibrated, spectroscopically confirmed SNIa to date. Assuming a flat Universe, we obtain a joint constraint of $\Omega_M = 0.266^{+0.026}_{-0.016}(stat 1\sigma)$, and $w = -1.112^{+0.069}_{-0.072}(stat 1\sigma)$. These measurements are consistent with a cosmological constant.Physic