arXiv subjects

Eckhart Spalding

Publications and source records attributed to Eckhart Spalding.

26 records · Page 2Linked to original sources

arXiv2019

High Spatial Resolution Thermal-Infrared Spectroscopy with ALES: Resolved Spectra of the Benchmark Brown Dwarf Binary HD 130948BC

We present 2.9-4.1 micron integral field spectroscopy of the L4+L4 brown dwarf binary HD 130948BC, obtained with the Arizona Lenslets for Exoplanet Spectroscopy (ALES) mode of the Large Binocular Telescope Interferometer (LBTI). The HD 130948 system is a hierarchical triple system, in which the G2V primary is joined by two co-orbiting brown dwarfs. By combining the age of the system with the dynamical masses and luminosities of the substellar companions, we can test evolutionary models of cool brown dwarfs and extra-solar giant planets. Previous near-infrared studies suggest a disagreement between HD 130948BC luminosities and those derived from evolutionary models. We obtained spatially-resolved, low-resolution (R~20) L-band spectra of HD 130948B and C to extend the wavelength coverage into the thermal infrared. Jointly using JHK photometry and ALES L-band spectra for HD 130948BC, we derive atmospheric parameters that are consistent with parameters derived from evolutionary models. We leverage the consistency of these atmospheric quantities to favor a younger age (0.50 \pm 0.07 Gyr) of the system compared to the older age (0.79 \pm 0.22 Gyr) determined with gyrochronology in order to address the luminosity discrepancy.

astro-ph.SR↗

arXiv2018

The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions

We present the results of the largest $L^{\prime}$ ($3.8~μ$m) direct imaging survey for exoplanets to date, the Large Binocular Telescope Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98 stars with spectral types from B to M. Cool planets emit a larger share of their flux in $L^{\prime}$ compared to shorter wavelengths, affording LEECH an advantage in detecting low-mass, old, and cold-start giant planets. We emphasize proximity over youth in our target selection, probing physical separations smaller than other direct imaging surveys. For FGK stars, LEECH outperforms many previous studies, placing tighter constraints on the hot-start planet occurrence frequency interior to $\sim20$ au. For less luminous, cold-start planets, LEECH provides the best constraints on giant-planet frequency interior to $\sim20$ au around FGK stars. Direct imaging survey results depend sensitively on both the choice of evolutionary model (e.g., hot- or cold-start) and assumptions (explicit or implicit) about the shape of the underlying planet distribution, in particular its radial extent. Artificially low limits on the planet occurrence frequency can be derived when the shape of the planet distribution is assumed to extend to very large separations, well beyond typical protoplanetary dust-disk radii ($\lesssim50$ au), and when hot-start models are used exclusively. We place a conservative upper limit on the planet occurrence frequency using cold-start models and planetary population distributions that do not extend beyond typical protoplanetary dust-disk radii. We find that $\lesssim90\%$ of FGK systems can host a 7 to 10 $M_{\mathrm{Jup}}$ planet from 5 to 50 au. This limit leaves open the possibility that planets in this range are common.

astro-ph.EP↗

arXiv2018

The Extremely Luminous Quasar Survey (ELQS) in the Sloan Digital Sky Survey footprint. II. The North Galactic Cap Sample

We present the North Galactic Cap sample of the Extremely Luminous Quasar Survey (ELQS-N), which targets quasars with $M_{1450}<-27$ at $2.8 \leq z < 5$ in an area of $\sim7600\,\rm{deg}^2$ of the Sloan Digital Sky Survey (SDSS) footprint with $90\text{\textdegree}<\rm{RA}<270\text{\textdegree}$. Based on a near-infrared/infrared \textit{JKW2} color cut, the ELQS selection efficiently uses random forest methods to classify quasars and to estimate photometric redshifts; this scheme overcomes some of the difficulties of pure optical quasar selection at $z\approx3$. As a result, we retain a completeness of $>70\%$ over $z\sim3.0-5.0$ at $m_{i}\lesssim17.5$, limited toward fainter magnitudes by the depth of the Two Micron All Sky Survey (2MASS). The presented quasar catalog consists of a total of 270 objects, of which 39 are newly identified in this work with spectroscopy obtained at the Vatican Advanced Technology Telescope and the MMT $6.5\,\rm{m}$ telescope. In addition to the high completeness, which allowed us to discover new quasars in the already well-surveyed SDSS North Galactic Cap, the efficiency of our selection is relatively high at $\sim79\%$. Using 120 objects of this quasar sample we are able to extend the previously measured optical quasar luminosity function (QLF) by one magnitude toward the bright end at $2.8 \leq z \leq 4.5$. A first analysis of the QLF suggests a relatively steep bright-end slope of $β\approx-4$ for this sample. This result contrasts with previous results in the same redshift range, which find a much flatter slope around $β\sim-2.5$, but agrees with recent measurements of the bright-end slope at lower and higher redshifts. Our results constrain the bright-end slope at $z=2.8-4.5$ to $β<-2.94$ with a 99\% confidence.

astro-ph.GA↗

arXiv2018

The TRENDS High-Contrast Imaging Survey. VII. Discovery of a Nearby Sirius-like White Dwarf System (HD 169889)

Monitoring the long-term radial velocity (RV) and acceleration of nearby stars has proven an effective method for directly detecting binary and substellar companions. Some fraction of nearby RV trend systems are expected to be comprised of compact objects that likewise induce a systemic Doppler signal. In this paper, we report the discovery of a white dwarf companion found to orbit the nearby ($π= 28.297 \pm 0.066$ mas) G9 V star HD 169889. High-contrast imaging observations using NIRC2 at Keck and LMIRCam at the LBT uncover the ($ΔH = 9.76 \pm 0.16$, $ΔL' = 9.60 \pm 0.03$) companion at an angular separation of 0.8'' (28 au). Thirteen years of precise Doppler observations reveal a steep linear acceleration in RV time series and place a dynamical constraint on the companion mass of $M \geq 0.369 \pm 0.010 M_{\odot}$. This "Sirius-like" system adds to the census of white dwarf companions suspected to be missing in the solar neighborhood.

astro-ph.SR↗

arXiv2018

Towards controlled Fizeau observations with the Large Binocular Telescope

The Large Binocular Telescope Interferometer (LBTI) can perform Fizeau interferometry in the focal plane, which accesses spatial information out to the LBT's full 22.7-m edge-to-edge baseline. This mode has previously been used to obtain science data, but has been limited to observations where the optical path difference (OPD) between the two beams is not controlled, resulting in unstable fringes on the science detectors. To maximize the science return, we are endeavoring to stabilize the OPD and tip-tilt variations and make the LBTI Fizeau mode optimized and routine. Here we outline the optical configuration of LBTI's Fizeau mode and our strategy for commissioning this observing mode.

astro-ph.IM↗

arXiv2017

Precision Time-series Photometry in the Thermal Infrared with a 'Wall-Eyed' Pointing Mode at the Large Binocular Telescope

Time-series photometry taken from ground-based facilities is improved with the use of comparison stars due to the short timescales of atmospheric-induced variability. However, the sky is bright in the thermal infrared (3-5 um), and the correspondingly small fields-of-view of available detectors make it highly unusual to have a calibration star in the same field as a science target. Here we present a new method of obtaining differential photometry by simultaneously imaging a science target and a calibrator star, separated by <2 amin, onto a 10x10 asec field-of-view detector. We do this by taking advantage of the LBT's unique binocular design to point the two co-mounted telescopes apart and simultaneously obtain both targets in three sets of observations. Results indicate that the achievable scatter in Ls-band (3.3 um) is at the percent level for bright targets, and possibly better with heavier sampling and characterization of the systematics.

astro-ph.IM↗

arXiv2016

Imaging protoplanets: observing transition disks with non-redundant masking

Transition disks, protoplanetary disks with inner clearings, are promising objects in which to directly image forming planets. The high contrast imaging technique of non-redundant masking is well posed to detect planetary mass companions at several to tens of AU in nearby transition disks. We present non-redundant masking observations of the T Cha and LkCa 15 transition disks, both of which host posited sub-stellar mass companions. However, due to a loss of information intrinsic to the technique, observations of extended sources (e.g. scattered light from disks) can be misinterpreted as moving companions. We discuss tests to distinguish between these two scenarios, with applications to the T Cha and LkCa 15 observations. We argue that a static, forward-scattering disk can explain the T Cha data, while LkCa 15 is best explained by multiple orbiting companions.

astro-ph.EP↗

arXiv2013

Panning for RRL Nuggets in the SDSS-DR9, Single Epoch Spectra

The SDSS has been a gold mine for understanding properties of the Milky Way. Below, in the watershed, there remain small nuggets to be found flowing from the deepest recesses of the mine. The SDSS-DR9 included the release of the flux- and wavelength-calibrated, individual spectra which were subsequently combined to form the composite spectra found in previous SDSS data releases. These single-epoch spectra (SES) can be analyzed to find flux and spectral line variability, and to probe aspects of phase variations for objects such as RRL stars. For $\sim 45%$ of the spectra in the RRL color range, SES were taken on separate nights, sometimes weeks apart. The remaining dataset have a time baseline of 0.75 to 1.5 hours and consist of 4-7 separate exposures. In my talk I will present details of our project to detect variability and to constrain the pulsation phase at the time of observation. I will discuss our auto-detection technique that uses division of all SES for a given star to search for variations in the flux, the hydrogen Balmer lines and the CaII K line. This procedure is being tested against known variables and non-variable stars within Stripe 82 to determine the identification effectiveness as a function of signal-to-noise, RRL type, and time baseline length. I will also discuss the use of empirical standard star templates to predict pulsation phase from the combination of hydrogen line strengths and radial velocity variations. Our ultimate goal is to combine the SES analysis with our new metallicity calibration in order to increase the number of RRL stars that have reliable metallicity determinations and which can then be used to probe the structure of the Milky Way halo.

astro-ph.SR↗