John S. de Groot

MARVELS-1b: A Short-period, Brown Dwarf Desert Candidate from the SDSS-III Marvels Planet Search

We present a new short-period brown dwarf (BD) candidate around the star TYC 1240-00945-1. This candidate was discovered in the first year of the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the Sloan Digital Sky Survey (SDSS) III, and we designate the BD as MARVELS-1b. MARVELS uses the technique of dispersed fixed-delay interferometery to simultaneously obtain radial velocity (RV) measurements for 60 objects per field using a single, custom-built instrument that is fiber fed from the SDSS 2.5 m telescope. From our 20 RV measurements spread over a ~370 day time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 2.533 ± 0.025 km s^(–1), period P = 5.8953 ± 0.0004 days, and eccentricity consistent with circular. Independent follow-up RV data confirm the orbit. Adopting a mass of 1.37 ± 0.11 M_☉ for the slightly evolved F9 host star, we infer that the companion has a minimum mass of 28.0 ± 1.5 M_(Jup), a semimajor axis 0.071 ± 0.002 AU assuming an edge-on orbit, and is probably tidally synchronized. We find no evidence for coherent intrinsic variability of the host star at the period of the companion at levels greater than a few millimagnitudes. The companion has an a priori transit probability of ~14%. Although we find no evidence for transits, we cannot definitively rule them out for companion radii ≲ R_(Jup).

A new generation multi-object Doppler instrument for the SDSS-III Multi-object APO Radial Velocity Exoplanet Large-area Survey

We report performance of a new generation multi-object Doppler instrument for the on-going Multi-object APO Radial-velocity Exoplanet Large-area Survey (MARVELS) of the Sloan Digital Sky Survey III (SDSS-III) program. This instrument is based on dispersed fixed-delay interferomtry design. It consists of a multi-object fiber-feed, a thermally compensated monolithic fixed-delay interferometer, a high throughput spectrograph and a 4kx4k CCD camera. The spectrograph resolving power is R=11,000 and the wavelength coverage is 500-570 nm. The instrument is capable of measuring 60 stars in a single exposure for high to moderate precision radial velocity (3-20 m/s) measurements depending on the star magnitudes (V=7.6-12). The instrument was commissioned at the SDSS telescope in September 2008 and used to collect science data starting in October 2008. Observations of reference stars show that the measured photon noise limiting errors are consistent with the prediction for most of the measurements.

Design, performance, and early results from extremely high Doppler precision instruments in a global network

We report design, performance and early results from two of the Extremely High Precision Extrasolar Planet Tracker Instruments (EXPERT) as part of a global network for hunting for low mass planets in the next decade. EXPERT is a combination of a thermally compensated monolithic Michelson interferometer and a cross-dispersed echelle spectrograph for extremely high precision Doppler measurements for nearby bright stars (e.g., 1m/s for a V=8 solar type star in 15 min exposure). It has R=18,000 with a 72 micron slit and a simultaneous coverage of 390-694 nm. The commissioning results show that the instrument has already produced a Doppler precision of about 1 m/s for a solar type star with S/N~100 per pixel. The instrument has reached ~4 mK (P-V) temperature stability, ~1 mpsi pressure stability over a week and a total instrument throughput of ~30% at 550 nm from the fiber input to the detector. EXPERT also has a direct cross-dispersed echelle spectroscopy mode fed with 50 micron fibers. It has spectral resolution of R=27,000 and a simultaneous wavelength coverage of 390-1000 nm.

The optical design of MARVELS spectrograph

This paper describes an optical spectrograph design for the Multi-object APO Radial-Velocity Exoplanet Large-area Survey (MARVELS) instrument. This MARVELS instrument is currently installed at the Sloan 2.5m telescope, and is capable of simultaneously monitoring 60 stars at high radial velocity precision for a planet survey. The MARVELS spectrograph consists of an entrance slit (multi-slits), collimator optics, a Volume Phase Holographic (VPH) grating, camera optics and a 4kx4k CCD camera, which with a 160mm diameter collimated beam provides a spectral resolution of R =10000. This spectrograph is transmissive and optimized for delivering high throughput and high image quality over the entire operation bandwidth 500-570nm and the whole 160mmx30mm square shape FOV. The collimator and camera optics (280 mm largest diameter) are all made of standard optical grade glasses. The f/4 input beams from the MARVELS monolithic interferometer are converted to f/1.5 beams on the detector by this spectrograph, and form 120 stellar fringe spectra.

Design and Performance of a New Generation, Compact, Low Cost, Very High Doppler Precision and Resolution Optical Spectrograph

This paper is to report the design and performance of a very high Doppler precision cross-dispersed echelle spectrograph, EXtremely high Precision ExtrasolaR planet Tracker III (EXPERT-III), as part of a global Exoplanet Tracker (ET) network. The ET network is designed to hunt low mass planets, especially habitable rocky planets, around GKM dwarfs. It has an extremely high spectral resolution (EHR) mode of R=110,000 and a high resolution (HR) mode of R=56,000 and can simultaneously cover 0.38-0.9 μm with a 4kx4k back-illuminated Fairchild CCD detector with a single exposure. EXPERT-III is optimized for high throughput by using two-prisms cross-disperser and a large core diameter fiber (2 arcsec on sky, or 80 μm at f/4) to collect photons from the Kitt Peak National Observatory (KPNO) 2.1m telescope. The average overall detection efficiency is ~6% from above the atmosphere to the detector for the EHR Mode and about 11% for the HR mode. The extremely high spectral resolution in a compact design (the spectrograph dimension, 1.34x0.8x0.48 m) is realized by coupling the single input 80 μm telescope fiber into four 40 μm fibers and re-arranging the four small core diameter fibers into a linear fiber slit array (a one-to-four fiber image slicer). EXPERT-III is operated in a vacuum chamber with temperature controlled to ~2 milli-Kelvin rms for an extended period of time. The radial velocity (RV) drift is controlled to within 10 meters/second (m/s) over a month. EXPERT-III can reach a photon noise limited RV measurement precision of ~0.3 m/s for a V=8 mag GKM type dwarf with small rotation (vsini =2 km/s) in a 15 min exposure. EXPERT-III’s RV measurement uncertainties for bright stars are primarily limited by the Thorium-Argon (ThAr) calibration source (~0.5 m/s). EXPERT-III will serve as an excellent public accessible high resolution optical spectroscope facility at the KPNO 2.1m telescope.

Design of a near-IR Doppler instrument for planet searches

Doppler searches are extending to the near infrared to detect and characterize habitable planets around low mass stars. We present an optical design and performance of a near-IR Doppler instrument. This instrument has two operating modes covering 0.8-1.8 microns. One mode is called IRET, which consists of a fix-delay interferometer and a crossdispersed echelle spectrograph to simultaneously cover 0.8-1.35 microns with a spectral resolution of R=22000 on a 2k x 2k H2RG IR array. The other mode is called FIRST, which uses a silicon immersion grating as the main disperser to simultaneously cover 1.4-1.8 microns with a spectral resolution of R=55000 on the same detector as IRET. The triplepass parabola white pupil design is used to restrain background scatter radiation with stable configuration for precision radial velocity measurements. We used high index standard glasses for camera optics and VPH gratings as crossdispersers in both modes. The FIRST mode can be switched in and out conveniently while the IRET mode is kept without moving parts to increase its stability. This instrument is designed to deliver up to 1 m/s Doppler precision RV measurements of nearby bright M dwarfs at the Apache Point Observatory 3.5 meter telescope. The instrument is expected to be operational in the spring 2011.

Optical design of a double pass cross-dispersed echelle spectrograph for extremely high precision extrasolar planet trackers

We describe the optical design and performance of a cross-dispersed echelle spectrograph designed to deliver high precision radial velocities. The spectrograph design enables two working modes, a Radial Velocity Mode (RVM) and a Direct Echelle Mode (DEM). The spectra resolving power of the RVM is R=18000 over 390nm-690nm when used with 1 arcsec slit, and delivering a R=27000 over 390nm-1000nm while using 0.6 arcsec slit for DEM. The focal ratio of this spectrograph is f/4 and the collimated beam diameter is 85mm. An R2 Echelle with 87 l/mm groove density and a 63 degree normal blaze angle will be used as the main disperse grating. A 45 degree PBM2Y prism operated in a double pass serves as a cross-disperser to separate the dispersion orders. Two objects spectra will be recorded on the top and bottom half of the one 4k by 4k CCD (15-micron pixel size) respectively in RVM, while one object spectra will be recorded on the same entire CCD. The total throughput of this spectrograph, in which consists of all spherical surface lenses is around 60%.