arXiv subjects

Howard Isaacson

Publications and source records attributed to Howard Isaacson.

At least 217 records · Page 12Linked to original sources

arXiv2018

The Breakthrough Listen Search for Intelligent Life: Wide-bandwidth Digital Instrumentation for the CSIRO Parkes 64-m Telescope

Breakthrough Listen is a ten-year initiative to search for signatures of technologies created by extraterrestrial civilizations at radio and optical wavelengths. Here, we detail the digital data recording system deployed for Breakthrough Listen observations at the 64-m aperture CSIRO Parkes Telescope in New South Wales, Australia. The recording system currently implements two recording modes: a dual-polarization, 1.125 GHz bandwidth mode for single beam observations, and a 26-input, 308-MHz bandwidth mode for the 21-cm multibeam receiver. The system is also designed to support a 3 GHz single-beam mode for the forthcoming Parkes ultra-wideband feed. In this paper, we present details of the system architecture, provide an overview of hardware and software, and present initial performance results.

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arXiv2018

Retired A Stars and Their Companions VIII: 15 New Planetary Signals Around Subgiants and Transit Parameters for California Planet Search Planets with Subgiant Hosts

We present the discovery of 7 new planets and 8 planet candidates around subgiant stars, as additions to the known sample of planets around "retired A stars" (Johnson et al. 2006). Among these are the possible first 3-planet systems around subgiant stars, HD 163607 and HD 4917. Additionally, we present calculations of possible transit times, durations, depths, and probabilities for all known planets around subgiant (3 < log g < 4) stars, focused on possible transits during the TESS mission. While most have transit probabilities of 1-2%, we find that there are 3 planets with transit probabilities > 9%.

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arXiv2018

Deep exploration of $ε$ Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet

We present the most sensitive direct imaging and radial velocity (RV) exploration of $ε$ Eridani to date. $ε$ Eridani is an adolescent planetary system, reminiscent of the early Solar system. It is surrounded by a prominent and complex debris disk which is likely stirred by one or several gas giant exoplanets. The discovery of the RV signature of a giant exoplanet was announced 15 years ago, but has met with scrutiny due to possible confusion with stellar noise. We confirm the planet with a new compilation and analysis of precise RV data spanning 30 years, and combine it with upper limits from our direct imaging search, the most sensitive ever performed. The deep images were taken in the Ms band (4.7$μ$m) with the vortex coronagraph recently installed in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive window for planet searches around nearby adolescent systems. The RV data and direct imaging upper limit maps were combined in an innovative joint Bayesian analysis, providing new constraints on the mass and orbital parameters of the elusive planet. $ε$ Eridani b has a mass of $0.78^{+0.38}_{-0.12}$ $M_{Jup}$ and is orbiting $ε$ Eridani at about $3.48\pm 0.02$ AU with a period of $7.37 \pm 0.07$ years. The eccentricity of $ε$ Eridani b's orbit is $0.07^{+0.06}_{-0.05}$, an order of magnitude smaller than early estimates and consistent with a circular orbit. We discuss our findings from the standpoint of planet-disk interactions and prospects for future detection and characterization with the James Webb Space Telescope.

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arXiv2018

60 Validated Planets from K2 Campaigns 5-8

We present a uniform analysis of 155 candidates from the second year of NASA's $K2$ mission (Campaigns 5-8), yielding 60 statistically validated planets spanning a range of properties, with median values of $R_p$ = 2.5 $R_\oplus$, $P$ = 7.1 d, $T_\mathrm{eq}$ = 811 K, and $J$ = 11.3 mag. The sample includes 24 planets in 11 multi-planetary systems, as well as 18 false positives, and 77 remaining planet candidates. Of particular interest are 18 planets smaller than 2 $R_\oplus$, five orbiting stars brighter than $J$ = 10 mag, and a system of four small planets orbiting the solar-type star EPIC 212157262. We compute planetary transit parameters and false positive probabilities using a robust statistical framework and present a complete analysis incorporating the results of an intensive campaign of high resolution imaging and spectroscopic observations. This work brings the $K2$ yield to over 360 planets, and by extrapolation we expect that $K2$ will have discovered $\sim$600 planets before the expected depletion of its on-board fuel in late 2018.

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arXiv2018

HD 202772A B: A Transiting Hot Jupiter Around A Bright, Mildly Evolved Star In A Visual Binary Discovered By Tess

We report the first confirmation of a hot Jupiter discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HD 202772A b. The transit signal was detected in the data from TESS Sector 1, and was confirmed to be of planetary origin through radial-velocity measurements. HD 202772A b is orbiting a mildly evolved star with a period of 3.3 days. With an apparent magnitude of V = 8.3, the star is among the brightest known to host a hot Jupiter. Based on the 27days of TESS photometry, and radial velocity data from the CHIRON and HARPS spectrographs, the planet has a mass of 1.008+/-0.074 M_J and radius of 1.562+/-0.053 R_J , making it an inflated gas giant. HD 202772A b is a rare example of a transiting hot Jupiter around a quickly evolving star. It is also one of the most strongly irradiated hot Jupiters currently known.

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arXiv2018

Kepler-1656b: a Dense Sub-Saturn With an Extreme Eccentricity

Kepler-1656b is a 5 $R_E$ planet with an orbital period of 32 days initially detected by the prime Kepler mission. We obtained precision radial velocities of Kepler-1656 with Keck/HIRES in order to confirm the planet and to characterize its mass and orbital eccentricity. With a mass of $48 \pm 4 M_E$, Kepler-1656b is more massive than most planets of comparable size. Its high mass implies that a significant fraction, roughly 80%, of the planet's total mass is in high density material such as rock/iron, with the remaining mass in a low density H/He envelope. The planet also has a high eccentricity of $0.84 \pm 0.01$, the largest measured eccentricity for any planet less than 100 $M_E$. The planet's high density and high eccentricity may be the result of one or more scattering and merger events during or after the dispersal of the protoplanetary disk.

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arXiv2018

Radial velocities from the N2K Project: 6 new cold gas giant planets orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810

The N2K planet search program was designed to exploit the planet-metallicity correlation by searching for gas giant planets orbiting metal-rich stars. Here, we present the radial velocity measurements for 378 N2K target stars that were observed with the HIRES spectrograph at Keck Observatory between 2004 and 2017. With this data set, we announce the discovery of six new gas giant exoplanets: a double-planet system orbiting HD 148164 ($M \sin i$ of 1.23 and 5.16 M$_{\rm JUP}$) and single planet detections around HD 55696 ($M \sin i$ = 3.87 M$_{\rm JUP}$), HD 98736 ($M \sin i$ = 2.33 M$_{\rm JUP}$), HD 203473 ($M \sin i$ = 7.8 M$_{\rm JUP}$), and HD 211810 ($M \sin i$ = 0.67 M$_{\rm JUP}$). These gas giant companions have orbital semi-major axes between 1.0 and 6.2 AU and eccentricities ranging from 0.13 to 0.71. We also report evidence for three gravitationally bound companions with $M \sin i$ between 20 to 30 M$_{\rm JUP}$, placing them in the mass range of brown dwarfs, around HD 148284, HD 214823, and HD 217850, and four low mass stellar companions orbiting HD 3404, HD 24505, HD 98630, and HD 103459. In addition, we present updated orbital parameters for 42 previously announced planets. We also report a nondetection of the putative companion HD 73256 b. Finally, we highlight the most promising candidates for direct imaging and astrometric detection, and find that many hot Jupiters from our sample could be detectable by state-of-the-art telescopes such as Gaia.

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arXiv2018

Some Bright Stars with Smooth Continua for Calibrating the Response of High Resolution Spectrographs

When characterizing a high resolution echelle spectrograph, for instance for precise Doppler work, it is useful to observe featureless sources such as quartz lamps or hot stars to determine the response of the instrument. Such sources provide a way to determine the blaze function of the orders, pixel-to-pixel variations in the detector, fringing in the system, and other important characteristics. In practice, however, many B or early A stars do not provide a smooth continuum, whether because they are not rotating rapidly enough or for some other reason. In fact, we have found that published rotational velocities and temperatures are not a specific and sensitive guide to whether a star's continuum will be smooth. A useful resource for observers, therefore, is a list of "good" hot stars: bright, blue stars known empirically to have no lines or other spectral features beyond the Balmer series with minima below 95% of the continuum. We have compiled a list of such stars visible from Northern Hemisphere telescopes. This list includes all stars listed in the Yale Bright Star Catalog (Hoffleit & Jaschek 1991) as being single with V < 5.5, v sin i > 175 km/s, and declination > -30, and many other hot stars that we have found useful for calibration purposes. The list here of "bad" stars may also be of interest in studies of hot, slowly rotating stars.

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arXiv2018

Two warm, low-density sub-Jovian planets orbiting bright stars in K2 campaigns 13 and 14

We report the discovery of two planets transiting the bright stars HD 89345 (EPIC 248777106, $V=9.376$, $K=7.721$) in K2 Campaign 14 and HD 286123 (EPIC 247098361, $V=9.822$, $K=8.434$) in K2 Campaign 13. Both stars are G-type stars, one of which is at or near the end of its main sequence lifetime, and the other that is just over halfway through its main sequence lifetime. HD 89345 hosts a warm sub-Saturn (0.66 $R_J$, 0.11 $M_J$, $T_\mathrm{eq}=1100$ K) in an 11.81-day orbit. The planet is similar in size to WASP-107b, which falls in the transition region between ice giants and gas giants. HD 286123 hosts a Jupiter-sized, low-mass planet (1.06 $R_J$, 0.39 $M_J$, $T_\mathrm{eq}=1000$ K) in an 11.17-day, mildly eccentric orbit, with $e=0.255\pm0.035$. Given that they orbit relatively evolved main-sequence stars and have orbital periods longer than 10 days, these planets are interesting candidates for studies of gas planet evolution, migration, and (potentially) re-inflation. Both planets have spent their entire lifetimes near the proposed stellar irradiation threshold at which giant planets become inflated, and neither shows any sign of radius inflation. They probe the regime where inflation begins to become noticeable and are valuable in constraining planet inflation models. In addition, the brightness of the host stars, combined with large atmospheric scale heights of the planets, makes these two systems favorable targets for transit spectroscopy to study their atmospheres and perhaps provide insight into the physical mechanisms that lead to inflated hot Jupiters.

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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.

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arXiv2018

Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars III: A High Mass & Low Envelope Fraction for the Warm Neptune K2-55b

K2-55b is a Neptune-sized planet orbiting a K7 dwarf with a radius of $0.715^{+0.043}_{-0.040}R_\odot$, a mass of $0.688\pm0.069 M_\odot$, and an effective temperature of $4300^{+107}_{-100}$K. Having characterized the host star using near-infrared spectra obtained at IRTF/SpeX, we observed a transit of K2-55b with Spitzer/IRAC and confirmed the accuracy of the original K2 ephemeris for future follow-up transit observations. Performing a joint fit to the Spitzer/IRAC and K2 photometry, we found a planet radius of $4.41^{+0.32}_{-0.28} R_\oplus$, an orbital period of $2.84927265_{-6.42\times10^{-6}}^{+6.87\times10^{-6}}$ days, and an equilibrium temperature of roughly 900K. We then measured the planet mass by acquiring twelve radial velocity (RV) measurements of the system using HIRES on the 10m Keck I Telescope. Our RV data set precisely constrains the mass of K2-55b to $43.13^{+5.98}_{-5.80} M_\oplus$, indicating that K2-55b has a bulk density of $2.8_{-0.6}^{+0.8}$ g cm$^{-3}$ and can be modeled as a rocky planet capped by a modest H/He envelope ($M_{\rm envelope} = 12\pm3\% M_p$). K2-55b is denser than most similarly sized planets, raising the question of whether the high planetary bulk density of K2-55b could be attributed to the high metallicity of K2-55. The absence of a substantial volatile envelope despite the large mass of K2-55b poses a challenge to current theories of gas giant formation. We posit that K2-55b may have escaped runaway accretion by migration, late formation, or inefficient core accretion or that K2-55b was stripped of its envelope by a late giant impact.

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arXiv2018

A 2 Earth Radius Planet Orbiting the Bright Nearby K-Dwarf Wolf 503

Since its launch in 2009, the Kepler telescope has found thousands of planets with radii between that of Earth and Neptune. Recent studies of the distribution of these planets have revealed a rift in the population near 1.5-2.0$R_{\bigoplus}$, informally dividing these planets into "super-Earths" and "sub-Neptunes". The origin of this division is not well understood, largely because the majority of planets found by Kepler orbit distant, dim stars and are not amenable to radial velocity follow-up or transit spectroscopy, making bulk density and atmospheric measurements difficult. Here, we present the discovery and validation of a newly found $2.03^{+0.08}_{-0.07}~R_{\bigoplus}$ planet in direct proximity to the radius gap, orbiting the bright ($J=8.32$~mag), nearby ($D=44.5$~pc) high proper motion star Wolf 503 (EPIC 212779563). We classify Wolf 503 as a K3.5V star and member of the thick disc population. We determine the possibility of a companion star and false positive detection to be extremely low using both archival images and high-contrast adaptive optics images from the Palomar observatory. The brightness of the host star makes Wolf 503b a prime target for prompt radial velocity follow-up, HST transit spectroscopy, as well as detailed atmospheric characterization with JWST. With its measured radius near the gap in the planet radius and occurrence rate distribution, Wolf 503b offers a key opportunity to better understand the origin of this radius gap as well as the nature of the intriguing populations of "super-Earths" and "sub-Neptunes" as a whole.

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arXiv2018

A TESS Dress Rehearsal: Planetary Candidates and Variables from K2 Campaign 17

We produce light curves for all ~34,000 targets observed with K2 in Campaign 17 (C17), identifying 34 planet candidates, 184 eclipsing binaries, and 222 other periodic variables. The location of the C17 field means follow-up can begin immediately now that the campaign has concluded and interesting targets have been identified. The C17 field has a large overlap with C6, so this latest campaign also offers a rare opportunity to study a large number of targets already observed in a previous K2 campaign. The timing of the C17 data release, shortly before science operations begin with the Transiting Exoplanet Survey Satellite (TESS), also lets us exercise some of the tools and methods developed for identification and dissemination of planet candidates from TESS. We find excellent agreement between these results and those identified using only K2-based tools. Among our planet candidates are several planet candidates with sizes < 4 R_E and orbiting stars with KepMag < 10 (indicating good RV targets of the sort TESS hopes to find) and a Jupiter-sized single-transit event around a star already hosting a 6 d planet candidate.

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arXiv2018

K2-231 b: A sub-Neptune exoplanet transiting a solar twin in Ruprecht 147

We identify a sub-Neptune exoplanet ($R_p = 2.5 \pm 0.2$ R$_\oplus$) transiting a solar twin in the Ruprecht 147 star cluster (3 Gyr, 300 pc, [Fe/H] = +0.1 dex). The ~81 day light curve for EPIC 219800881 (V = 12.71) from K2 Campaign 7 shows six transits with a period of 13.84 days, a depth of ~0.06%, and a duration of ~4 hours. Based on our analysis of high-resolution MIKE spectra, broadband optical and NIR photometry, the cluster parallax and interstellar reddening, and isochrone models from PARSEC, Dartmouth, and MIST, we estimate the following properties for the host star: $M_\star = 1.01 \pm 0.03$ M$_\odot$, $R_\star= 0.95 \pm 0.03$ R$_\odot$, and $T_{\rm eff} = 5695 \pm 50$ K. This star appears to be single, based on our modeling of the photometry, the low radial velocity variability measured over nearly ten years, and Keck/NIRC2 adaptive optics imaging and aperture-masking interferometry. Applying a probabilistic mass-radius relation, we estimate that the mass of this planet is $M_p = 7 +5 -3$ M$_\oplus$, which would cause a RV semi-amplitude of $K = 2 \pm 1$ m s$^{-1}$ that may be measurable with existing precise RV facilities. After statistically validating this planet with BLENDER, we now designate it K2-231 b, making it the second sub-stellar object to be discovered in Ruprecht 147 and the first planet; it joins the small but growing ranks of 23 other planets found in open clusters.

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arXiv2018

HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities

HAT-P-11 is a mid-K dwarf that hosts one of the first Neptune-sized planets found outside the solar system. The orbit of HAT-P-11b is misaligned with the star's spin --- one of the few known cases of a misaligned planet orbiting a star less massive than the Sun. We find an additional planet in the system based on a decade of precision radial velocity (RV) measurements from Keck/HIRES. HAT-P-11c is similar to Jupiter in its mass ($M_P \sin{i} = 1.6\pm0.1$ $M_J$) and orbital period ($P = 9.3^{+1.0}_{-0.5}$ year), but has a much more eccentric orbit ($e=0.60\pm0.03$). In our joint modeling of RV and stellar activity, we found an activity-induced RV signal of $\sim$7 m s$^{-1}$, consistent with other active K dwarfs, but significantly smaller than the 31 m s$^{-1}$ reflex motion due to HAT-P-11c. We investigated the dynamical coupling between HAT-P-11b and c as a possible explanation for HAT-P-11b's misaligned orbit, finding that planet-planet Kozai interactions cannot tilt planet b's orbit due to general relativistic precession; however, nodal precession operating on million year timescales is a viable mechanism to explain HAT-P-11b's high obliquity. This leaves open the question of why HAT-P-11c may have such a tilted orbit. At a distance of 38 pc, the HAT-P-11 system offers rich opportunities for further exoplanet characterization through astrometry and direct imaging.

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arXiv2018

Planetary Candidates from K2 Campaign 16

Given that Campaign 16 of the K2 mission is one of just two K2 campaigns observed so far in "forward-facing" mode, which enables immediate follow-up observations from the ground, we present a catalog of interesting targets identified through photometry alone. Our catalog includes 30 high-quality planet candidates (showing no signs of being non-planetary in nature), 48 more ambiguous events that may be either planets or false positives, 164 eclipsing binaries, and 231 other regularly periodic variable sources. We have released light curves for all targets in C16, and have also released system parameters and transit vetting plots for all interesting candidates identified in this paper. Of particular interest is a candidate planet orbiting the bright F dwarf HD 73344 (V=6.9, K=5.6) with an orbital period of 15 days. If confirmed, this object would correspond to a $2.56 \pm 0.18 \ R_\oplus$ planet and would likely be a favorable target for radial velocity characterization. This paper is intended as a rapid release of planet candidates, eclipsing binaries and other interesting periodic variables to maximize the scientific yield of this campaign, and as a test run for the upcoming TESS mission, whose frequent data releases call for similarly rapid candidate identification and efficient follow-up.

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arXiv2018

The Breakthrough Listen Search for Intelligent Life: 1.1-1.9 GHz observations of 692 Nearby Stars

We report on a search for engineered signals from a sample of 692 nearby stars using the Robert C. Byrd Green Bank Telescope, undertaken as part of the $Breakthrough~Listen~Initiative$ search for extraterrestrial intelligence. Observations were made over 1.1$-$1.9 GHz (L band), with three sets of five-minute observations of the 692 primary targets, interspersed with five-minute observations of secondary targets. By comparing the "ON" and "OFF" observations we are able to identify terrestrial interference and place limits on the presence of engineered signals from putative extraterrestrial civilizations inhabiting the environs of the target stars. During the analysis, eleven events passed our thresholding algorithm, but a detailed analysis of their properties indicates they are consistent with known examples of anthropogenic radio frequency interference. We conclude that, at the time of our observations, none of the observed systems host high-duty-cycle radio transmitters emitting between 1.1 and 1.9 GHz with an Equivalent Isotropic Radiated Power of $\sim10^{13}$ W, which is readily achievable by our own civilization. Our results suggest that fewer than $\sim$ 0.1$\%$ of the stellar systems within 50 pc possess the type of transmitters searched in this survey.

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arXiv2018

Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog With Measured Completeness and Reliability Based on Data Release 25

We present the Kepler Object of Interest (KOI) catalog of transiting exoplanets based on searching four years of Kepler time series photometry (Data Release 25, Q1-Q17). The catalog contains 8054 KOIs of which 4034 are planet candidates with periods between 0.25 and 632 days. Of these candidates, 219 are new and include two in multi-planet systems (KOI-82.06 and KOI-2926.05), and ten high-reliability, terrestrial-size, habitable zone candidates. This catalog was created using a tool called the Robovetter which automatically vets the DR25 Threshold Crossing Events (TCEs, Twicken et al. 2016). The Robovetter also vetted simulated data sets and measured how well it was able to separate TCEs caused by noise from those caused by low signal-to-noise transits. We discusses the Robovetter and the metrics it uses to sort TCEs. For orbital periods less than 100 days the Robovetter completeness (the fraction of simulated transits that are determined to be planet candidates) across all observed stars is greater than 85%. For the same period range, the catalog reliability (the fraction of candidates that are not due to instrumental or stellar noise) is greater than 98%. However, for low signal-to-noise candidates between 200 and 500 days around FGK dwarf stars, the Robovetter is 76.7% complete and the catalog is 50.5% reliable. The KOI catalog, the transit fits and all of the simulated data used to characterize this catalog are available at the NASA Exoplanet Archive.

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