arXiv subjects

Rebecca Oppenheimer

Publications and source records attributed to Rebecca Oppenheimer.

59 records · Page 4Linked to original sources

arXiv2015

Know the Star, Know the Planet. V. Characterization of the Stellar Companion to the Exoplanet Host HD 177830

HD 177830 is an evolved K0IV star with two known exoplanets. In addition to the planetary companions it has a late-type stellar companion discovered with adaptive optics imagery. We observed the binary star system with the PHARO near-IR camera and the Project 1640 coronagraph. Using the Project 1640 coronagraph and integral field spectrograph we extracted a spectrum of the stellar companion. This allowed us to determine that the spectral type of the stellar companion is a M4$\pm$1V. We used both instruments to measure the astrometry of the binary system. Combining these data with published data, we determined that the binary star has a likely period of approximately 800 years with a semi-major axis of 100-200 AU. This implies that the stellar companion has had little or no impact on the dynamics of the exoplanets. The astrometry of the system should continue to be monitored, but due to the slow nature of the system, observations can be made once every 5-10 years.

astro-ph.SR↗

arXiv2015

A New Method for Characterizing Very-Low-Mass Companions with Low Resolution Near-Infrared Spectroscopy

We present a new and computationally efficient method for characterizing very low mass companions using low resolution ($R\sim$30) near-infrared ($YJH$) spectra from high contrast imaging campaigns with integral field spectrograph (IFS) units. We conduct a detailed quantitative comparison of the efficacy of this method through tests on simulated data comparable in spectral coverage and resolution to the currently operating direct imaging systems around the world. In particular, we simulate Project 1640 data as an example of the use, accuracy, and precision of this technique. We present results from comparing simulated spectra of M, L, and T dwarfs with a large and finely-sampled grid of synthetic spectra using Markov Chain Monte Carlo techniques. We determine the precision and accuracy of effective temperature and surface gravity inferred from fits to PHOENIX dusty and cond, which we find reproduce the low-resolution spectra of all objects within the adopted flux uncertainties. Uncertainties in effective temperature decrease from $\pm$100-500 K for M dwarfs to as small as $\pm$30 K for some L and T spectral types. Surface gravity is constrained to within 0.2-0.4 dex for mid-L through T dwarfs, but uncertainties are as large as 1.0 dex or more for M dwarfs. Results for effective temperature from low-resolution $YJH$ spectra generally match predictions from published spectral type-temperature relationships except for L-T transition objects and young objects. Single-band spectra (i.e., narrower wavelength coverage) result in larger uncertainties and often discrepant results, suggesting that high contrast IFS observing campaigns can compensate for low spectral resolution by expanding the wavelength coverage for reliable characterization of detected companions. [Abstract truncated]

astro-ph.SR↗

arXiv2014

Direct Spectrum of the Benchmark T dwarf HD 19467 B

HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R~30 observations obtained simultaneously across the $JH$ bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5+/-1 dwarf with effective temperature Teff=$978^{+20}_{-43}$ K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.

astro-ph.SR↗

arXiv2014

Gemini Planet Imager Spectroscopy of the HR 8799 planets c and d

During the first-light run of the Gemini Planet Imager (GPI) we obtained K-band spectra of exoplanets HR 8799 c and d. Analysis of the spectra indicates that planet d may be warmer than planet c. Comparisons to recent patchy cloud models and previously obtained observations over multiple wavelengths confirm that thick clouds combined with horizontal variation in the cloud cover generally reproduce the planets' spectral energy distributions. When combined with the 3 to 4 um photometric data points, the observations provide strong constraints on the atmospheric methane content for both planets. The data also provide further evidence that future modeling efforts must include cloud opacity, possibly including cloud holes, disequilibrium chemistry, and super-solar metallicity.

astro-ph.EP↗

arXiv2014

S4: A Spatial-Spectral model for Speckle Suppression

High dynamic-range imagers aim to block out or null light from a very bright primary star to make it possible to detect and measure far fainter companions; in real systems a small fraction of the primary light is scattered, diffracted, and unocculted. We introduce S4, a flexible data-driven model for the unocculted (and highly speckled) light in the P1640 spectroscopic coronograph. The model uses Principal Components Analysis (PCA) to capture the spatial structure and wavelength dependence of the speckles but not the signal produced by any companion. Consequently, the residual typically includes the companion signal. The companion can thus be found by filtering this error signal with a fixed companion model. The approach is sensitive to companions that are of order a percent of the brightness of the speckles, or up to $10^{-7}$ times the brightness of the primary star. This outperforms existing methods by a factor of 2-3 and is close to the shot-noise physical limit.

astro-ph.IM↗