Direct Imaging of Exoplanets with Project 1640

Project 1640 is a suite of instrumentation and software focused on high-contrast imaging of exoplanets, probing the parameter space of companion size > 1MJ and distance 5-50 AU around the host stars. The instrument consists of an apodized Lyot coronagraph, with a Mach-Zender interferometer and an integral field spectrograph, forming data cubes of dimensions right ascension, declination, and wavelength. P1640 is operated at Palomar Observatory in Southern California, in conjunction with their PALM-3000 adaptive optics system. Data reduction models out remaining speckle noise using principle component analysis and produces a residual cube, which can then be manually inspected for possible companions. For this summer project, data reduction using the Karhunen-Lo ́eve Image Projection (KLIP) algorithm was completed on many of the survey stars and inspected, in an effort to search for more candidates. At this time, two possible candidates have been found, and are awaiting further confirmation

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 ∼ 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 ± 100–500 K for M dwarfs to as small as ± 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. We find that S/N ∼ 10 is sufficient to characterize temperature and gravity as well as possible given the model grid. Most relevant for direct-imaging campaigns targeting young primary stars is our finding that low-resolution near-infrared spectra of known young objects, compared to field objects of the same spectral type, result in similar best-fit surface gravities but lower effective temperatures, highlighting the need for better observational and theoretical understanding of the entangled effects of temperature, gravity, and dust on near-infrared spectra in cool low-gravity atmospheres

A deep search for planets in the inner 15 au around Vega

We present the results of a deep high-contrast imaging search for planets around Vega. Vega is an ideal target for high-contrast imaging because it is bright, nearby, and young with a face-on two-belt debris disk which may be shaped by unseen planets. We obtained $J-$ and $H-$band data on Vega with the coronagraphic integral-field spectrograph Project 1640 (P1640) at Palomar Observatory. Two nights of data were obtained in 2016, in poor seeing conditions, and two additional nights in more favorable conditions in 2017. In total, we obtained 5.5 hours of integration time on Vega in moderate to good seeing conditions (<1.5"). We did not detect any low mass companions in this system. Our data present the most sensitive contrast limits around Vega at very small separations (2-15 au) thus far, allowing us to place new constraints on the companions which may be sculpting the Vega system. In addition to new constraints, as the deepest data obtained with P1640, these observations form the final legacy of the now decommissioned instrument.Comment: Accepted for publication in A

Optimized modeling of Gaia-Hipparcos astrometry for the detection of the smallest cold Jupiter and confirmation of seven low mass companions

© 2021 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stab2225To fully constrain the orbits of low mass circumstellar companions, we conduct combined analyses of the radial velocity data as well as the Gaia and Hipparcos astrometric data for eight nearby systems. Our study shows that companion-induced position and proper motion differences between Gaia and Hipparcos are significant enough to constrain orbits of low mass companions to a precision comparable with previous combined analyses of direct imaging and radial velocity data. We find that our method is robust to whether we use Gaia DR2 or Gaia EDR3, as well as whether we use all of the data, or just proper motion differences. In particular, we fully characterize the orbits of HD 190360 b and HD 16160 C for the first time. With a mass of 1.8$\pm$0.2$m_{\rm Jup}$ and an effective temperature of 123-176 K and orbiting around a Sun-like star, HD 190360 b is the smallest Jupiter-like planet with well-constrained mass and orbit, belonging to a small sample of fully characterized Jupiter analogs. It is separated from its primary star by 0.25$''$ and thus may be suitable for direct imaging by the CGI instrument of the Roman Space Telescope.Peer reviewe

Pleiades or Not? Resolving the Status of the Lithium-rich M Dwarfs HHJ 339 and HHJ 430

Oppenheimer et al. discovered two M5 dwarfs in the Pleiades with nearly primordial lithium. These stars are not low enough in mass to represent the leading edge of the lithium depletion boundary at Pleiades age (~125 Myr). A possible explanation for the enhanced lithium in these stars is that they are actually not members of the Pleiades but instead are members of a younger moving group seen in projection toward the Pleiades. We have used data from Gaia DR2 to confirm that these two stars, HHJ 339 and HHJ 430, are indeed not members of the Pleiades. Based on their space motions, parallaxes, and positions in a Gaia-based color–magnitude diagram, it is probable that these two stars are about 40 parsecs foreground to the Pleiades and have ages of ~25 Myr. Kinematically they are best matched to the 32 Ori moving group

Point Source Polarimetry with the Gemini Planet Imager: Sensitivity Characterization with T5.5 Dwarf Companion HD 19467 B

Detecting polarized light from self-luminous exoplanets has the potential to provide key information about rotation, surface gravity, cloud grain size, and cloud coverage. While field brown dwarfs with detected polarized emission are common, no exoplanet or substellar companion has yet been detected in polarized light. With the advent of high contrast imaging spectro-polarimeters such as GPI and SPHERE, such a detection may now be possible with careful treatment of instrumental polarization. In this paper, we present 28 minutes of H-band GPI polarimetric observations of the benchmark T5.5 companion HD 19467 B. We detect no polarization signal from the target, and place an upper limit on the degree of linear polarization of p_(CL99.73%) ⩽ 2.4%. We discuss our results in the context of T dwarf cloud models and photometric variability