Claire Lamman, Christoph Baranec, Zachory K. Berta-Thompson, Nicholas M. Law, Jessica Schonhut-Stasik, Carl Ziegler, Maissa Salama, Rebecca Jensen-Clem, Dmitry A. Duev, Reed Riddle, Shrinivas R. Kulkarni, Jennifer G. Winters, Jonathan M. Irwin
Jan 16, 2020·astro-ph.SR·PDF We analyze observations from Robo-AO's field M dwarf survey taken on the 2.1m Kitt Peak telescope and perform a multiplicity comparison with Gaia DR2. Through its laser-guided, automated system, the Robo-AO instrument has yielded the largest adaptive optics M dwarf multiplicity survey to date. After developing an interface to visually identify and locate stellar companions, we selected eleven lowsignificance Robo-AO detections for follow-up on the Keck II telescope using NIRC2. In the Robo-AO survey we find 553 candidate companions within 4" around 534 stars out of 5566 unique targets, most of which are new discoveries. Using a position cross match with DR2 on all targets, we assess the binary recoverability of Gaia DR2 and compare the properties of multiples resolved by both Robo-AO and Gaia. The catalog of nearby M dwarf systems and their basic properties presented here can assist other surveys which observe these stars, such as the NASA TESS mission.
Chow-Choong Ngeow, Anupam Bhardwaj, Richard Dekany, Dmitry A. Duev, Matthew J. Graham, Steven L. Groom, Ashish A. Mahabal, Frank J. Masci, Michael S. Medford, Reed Riddle
Mar 28, 2022·astro-ph.SR·PDF Based on time-series observations collected from Zwicky Transient Facility (ZTF), we derived period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations for RR Lyrae located in globular clusters. We have applied various selection criteria to exclude RR Lyrae with problematic or spurious light curves. These selection criteria utilized information on the number of data points per light curve, amplitudes, colors, and residuals on the period-luminosity and/or period-Wesenheit relations. Due to blending, a number of RR Lyrae in globular clusters were found to be anomalously bright and have small amplitudes of their ZTF light curves. We used our final sample of ~750 RR Lyrae in 46 globular clusters covering a wide metallicity range (-2.36 < [Fe/H] < -0.54 dex) to derive PLZ and PWZ relations in gri bands. In addition, we have also derived the period-color-metallicity (PCZ) and for the first time, the PQZ relations where the Q-index is extinction-free by construction. We have compared our various relations to empirical and theoretical relations available in literature, and found a good agreement with most studies. Finally, we applied our derived PLZ relation to a dwarf galaxy, Crater II, and found its true distance modulus should be larger than the most recent determination.
Carl Ziegler, Nicholas M. Law, Christoph Baranec, Reed Riddle, Dmitry A. Duev, Ward Howard, Rebecca Jensen-Clem, S. R. Kulkarni, Tim Morton, Maïssa Salama
Dec 12, 2017·astro-ph.EP·PDF We present the overall statistical results from the Robo-AO Kepler planetary candidate survey, comprising of 3857 high-angular resolution observations of planetary candidate systems with Robo-AO, an automated laser adaptive optics system. These observations reveal previously unknown nearby stars blended with the planetary candidate host star which alter the derived planetary radii or may be the source of an astrophysical false positive transit signal. In the first three papers in the survey, we detected 440 nearby stars around 3313 planetary candidate host stars. In this paper, we present observations of 532 planetary candidate host stars, detecting 94 companions around 88 stars; 84 of these companions have not previously been observed in high-resolution. We also report 50 more-widely-separated companions near 715 targets previously observed by Robo-AO. We derive corrected planetary radius estimates for the 814 planetary candidates in systems with a detected nearby star. If planetary candidates are equally likely to orbit the primary or secondary star, the radius estimates for planetary candidates in systems with likely bound nearby stars increase by a factor of 1.54, on average. We find that 35 previously-believed rocky planet candidates are likely not rocky due to the presence of nearby stars. From the combined data sets from the complete Robo-AO KOI survey, we find that 14.5\pm0.5% of planetary candidate hosts have a nearby star with 4", while 1.2% have two nearby stars and 0.08% have three. We find that 16% of Earth-sized, 13% of Neptune-sized, 14% of Saturn-sized, and 19% of Jupiter-sized planet candidates have detected nearby stars.
Soumyadeep Bhattacharjee, S. R. Kulkarni, Albert K. H. Kong, M. S. Tam, Howard E. Bond, Kareem El-Badry, Ilaria Caiazzo, Nicholas Chornay, Matthew J. Graham, Antonio C. Rodriguez, Gregory R. Zeimann, Christoffer Fremling, Andrew J. Drake, Klaus Werner, Hector Rodriguez, Thomas A. Prince, Russ R. Laher, Tracy X. Chen, Reed Riddle
Over the past several decades, time-series photometry of CSPNe has yielded significant results including, but not limited to, discoveries of nearly 100 binary systems, insights into pulsations and winds in young white dwarfs, and studies of stars undergoing very late thermal pulses. We have undertaken a systematic study of optical photometric variability of cataloged CSPNe, using the light curves from the Zwicky Transient Facility (ZTF). By applying appropriate variability metrics, we arrive at a list of 94 highly variable CSPN candidates. Based on the timescales of the light-curve activity, we classify the variables broadly into short- and long-timescale variables. In this first paper in this series, we focus on the former, which is the majority class comprising 83 objects. We report periods for six sources for the first time, and recover several known periodic variables. Among the aperiodic sources, most exhibit a jitter around a median flux with a stable amplitude, and a few show outbursts. We draw attention to WeSb 1, which shows a different kind of variability: prominent deep and aperiodic dips, resembling transits from a dust/debris disk. We find strong evidence for a binary nature of WeSb 1 (possibly an F-type subgiant companion). The compactness of the emission lines and inferred high electron densities make WeSb 1 a candidate for either an EGB 6-type planetary nucleus, or a symbiotic system inside an evolved planetary nebula, both of which are rare objects. To demonstrate further promise with ZTF, we report three additional newly identified periodic sources that do not appear in the list of highly variable sources. Finally, we also introduce a two-dimensional metric space defined by the von Neumann statistics and Pearson Skew and demonstrate its effectiveness in identifying unique variables of astrophysical interest, like WeSb 1.
Christoph Baranec, Dani Atkinson, Reed Riddle, Donald Hall, Shane Jacobson, Nicholas M. Law, Mark Chun
Infrared avalanche photodiode arrays represent a panacea for many branches of astronomy by enabling extremely low-noise, high-speed and even photon-counting measurements at near-infrared wavelengths. We recently demonstrated the use of an early engineering-grade infrared avalanche photodiode array that achieves a correlated double sampling read noise of 0.73 e- in the lab, and a total noise of 2.52 e- on sky, and supports simultaneous high-speed imaging and tip-tilt wavefront sensing with the Robo-AO visible-light laser adaptive optics system at the Palomar Observatory 1.5-m telescope. We report here on the improved image quality achieved simultaneously at visible and infrared wavelengths by using the array as part of an image stabilization control-loop with adaptive-optics sharpened guide stars. We also discuss a newly enabled survey of nearby late M-dwarf multiplicity as well as future uses of this technology in other adaptive optics and high-contrast imaging applications.
Anna Y. Q. Ho, Daniel A. Perley, Yuhan Yao, Dmitry Svinkin, A. de Ugarte Postigo, R. A. Perley, D. Alexander Kann, Eric Burns, Igor Andreoni, Eric C. Bellm, Elisabetta Bissaldi, Joshua S. Bloom, Richard Dekany, Andrew J. Drake, José Feliciano Agüí Fernández, Dmitry Frederiks, Matthew J. Graham, Boyan A. Hristov, Mansi M. Kasliwal, S. R. Kulkarni, Harsh Kumar, Russ R. Laher, Alexandra L. Lysenko, Bagrat Mailyan, Christian Malacaria, A. A. Miller, S. Poolakkil, Reed Riddle, Anna Ridnaia, Ben Rusholme, Volodymyr Savchenko, Jesper Sollerman, Christina Thöne, Anastasia Tsvetkova, Mikhail Ulanov, Andreas von Kienlin
Jan 28, 2022·astro-ph.HE·PDF Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor $Γ_\mathrm{init}$ below the $Γ_\mathrm{init}\sim100$ required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors ($g-r>0$ mag), faint host galaxy ($r>23$ mag), and rapid fading ($dr/dt>1$ mag/day). Spectroscopy of the transient emission within a few days of discovery established cosmological distances ($z=0.876$ to $z=2.9$) for six events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a $γ$-ray trigger. Upon a retrospective search, four events (ZTF20abbiixp/AT2020kym, ZTF21aagwbjr/AT2021buv, ZTF21aakruew/AT2021cwd, ZTF21abfmpwn/AT2021qbd) turned out to have a likely associated LGRB (GRB200524A, GRB210204A, GRB210212B, GRB210610B), while three did not (ZTF20aajnksq/AT2020blt, ZTF21aaeyldq/AT2021any, ZTF21aayokph/AT2021lfa). Our search revealed no definitive new class of events: the simplest explanation for the apparently "orphan" events is that they were regular LGRBs missed by high-energy satellites due to detector sensitivity and duty cycle, although it is possible that they were intrinsically faint in $γ$-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing $γ$-rays and the material producing early optical afterglow emission, finding that they must be comparable.
Dmitry A. Duev, Bryce T. Bolin, Matthew J. Graham, Michael S. P. Kelley, Ashish Mahabal, Eric C. Bellm, Michael W. Coughlin, Richard Dekany, George Helou, Shrinivas R. Kulkarni, Frank J. Masci, Thomas A. Prince, Reed Riddle, Maayane T. Soumagnac, Stéfan J. van der Walt
Feb 26, 2021·astro-ph.IM·PDF We present Tails, an open-source deep-learning framework for the identification and localization of comets in the image data of the Zwicky Transient Facility (ZTF), a robotic optical time-domain survey currently in operation at the Palomar Observatory in California, USA. Tails employs a custom EfficientDet-based architecture and is capable of finding comets in single images in near real time, rather than requiring multiple epochs as with traditional methods. The system achieves state-of-the-art performance with 99% recall, 0.01% false positive rate, and 1-2 pixel root mean square error in the predicted position. We report the initial results of the Tails efficiency evaluation in a production setting on the data of the ZTF Twilight survey, including the first AI-assisted discovery of a comet (C/2020 T2) and the recovery of a comet (P/2016 J3 = P/2021 A3).
Chien-De Lee, Jia-Yu Ou, Po-Chieh Yu, Chow-Choong Ngeow, Po-Chieh Huang, Wing-Huen Ip, Franz-Josef Hambsch, Hyun-il Sung, Jan van Roestel, Richard Dekany, Andrew J. Drake, Matthew J. Graham, Dmitry A. Duev, Stephen Kaye, Thomas Kupfer, Russ R. Laher, Frank J. Masci, Przemek Mroz, James D. Neill, Reed Riddle, Ben Rusholme, Richard Walters
Feb 19, 2021·astro-ph.SR·PDF HO Puppis (HO Pup) was considered as a Be-star candidate based on its gamma-Cassiopeiae-type light curve, but lacked spectroscopic confirmation. Using distance measured from Gaia Data Release 2 and the spectral-energy-distribution (SED) fit on broadband photometry, the Be-star nature of HO Pup is ruled out. Furthermore, based on the 28,700 photometric data points collected from various time-domain surveys and dedicated intensive-monitoring observations, the light curves of HO Pup closely resemble IW And-type stars (as pointed out in Kimura et al. 2020a), exhibiting characteristics such as quasi-standstill phase, brightening, and dips. The light curve of HO Pup displays various variability timescales, including brightening cycles ranging from 23 to 61 days, variations with periods between 3.9 days and 50 minutes during the quasi-standstill phase, and a semi-regular ~14-day period for the dip events. We have also collected time-series spectra (with various spectral resolutions), in which Balmer emission lines and other expected spectral lines for an IW And-type star were detected (even though some of these lines were also expected to be present for Be stars). We detect Bowen fluorescence near the brightening phase, and that can be used to discriminate between IW And-type stars and Be stars. Finally, despite only observing for four nights, the polarization variation was detected, indicating that HO Pup has significant intrinsic polarization.
Benjamin J. Fulton, Karen A. Collins, B. Scott Gaudi, Keivan G. Stassun, Joshua Pepper, Thomas G. Beatty, Robert J. Siverd, Kaloyan Penev, Andrew W. Howard, Christoph Baranec, Giorgio Corfini, Jason D. Eastman, Joao Gregorio, Nicholas M. Law, Michael B. Lund, Thomas E. Oberst, Matthew T. Penny, Reed Riddle, Joseph E. Rodriguez, Daniel J. Stevens, Roberto Zambelli, Carl Ziegler, Allyson Bieryla, Giuseppe D`Ago, Darren L. DePoy, Eric L. N. Jensen, John F. Kielkopf, David W. Latham, Mark Manner, Jennifer Marshall, Kim K. McLeod, Phillip A. Reed
May 25, 2015·astro-ph.EP·PDF We announce the discovery of a highly inflated transiting hot Jupiter discovered by the KELT-North survey. A global analysis including constraints from isochrones indicates that the V = 10.8 host star (HD 343246) is a mildly evolved, G dwarf with $T_{\rm eff} = 5754_{-55}^{+54}$ K, $\log{g} = 4.078_{-0.054}^{+0.049}$, $[Fe/H] = 0.272\pm0.038$, an inferred mass $M_{*}=1.211_{-0.066}^{+0.078}$ M$_{\odot}$, and radius $R_{*}=1.67_{-0.12}^{+0.14}$ R$_{\odot}$. The planetary companion has mass $M_P = 0.867_{-0.061}^{+0.065}$ $M_{J}$, radius $R_P = 1.86_{-0.16}^{+0.18}$ $R_{J}$, surface gravity $\log{g_{P}} = 2.793_{-0.075}^{+0.072}$, and density $ρ_P = 0.167_{-0.038}^{+0.047}$ g cm$^{-3}$. The planet is on a roughly circular orbit with semimajor axis $a = 0.04571_{-0.00084}^{+0.00096}$ AU and eccentricity $e = 0.035_{-0.025}^{+0.050}$. The best-fit linear ephemeris is $T_0 = 2456883.4803 \pm 0.0007$ BJD$_{\rm TDB}$ and $P = 3.24406 \pm 0.00016$ days. This planet is one of the most inflated of all known transiting exoplanets, making it one of the few members of a class of extremely low density, highly-irradiated gas giants. The low stellar $\log{g}$ and large implied radius are supported by stellar density constraints from follow-up light curves, plus an evolutionary and space motion analysis. We also develop a new technique to extract high precision radial velocities from noisy spectra that reduces the observing time needed to confirm transiting planet candidates. This planet boasts deep transits of a bright star, a large inferred atmospheric scale height, and a high equilibrium temperature of $T_{eq}=1675^{+61}_{-55}$ K, assuming zero albedo and perfect heat redistribution, making it one of the best targets for future atmospheric characterization studies.
Dmitry A. Duev, Ashish Mahabal, Quanzhi Ye, Kushal Tirumala, Justin Belicki, Richard Dekany, Sara Frederick, Matthew J. Graham, George Helou, Russ R. Laher, Frank J. Masci, Thomas A. Prince, Reed Riddle, Philippe Rosnet, Maayane T. Soumagnac
Apr 11, 2019·astro-ph.IM·PDF We present DeepStreaks, a convolutional-neural-network, deep-learning system designed to efficiently identify streaking fast-moving near-Earth objects that are detected in the data of the Zwicky Transient Facility (ZTF), a wide-field, time-domain survey using a dedicated 47 sq. deg camera attached to the Samuel Oschin 48-inch Telescope at the Palomar Observatory in California, United States. The system demonstrates a 96-98% true positive rate, depending on the night, while keeping the false positive rate below 1%. The sensitivity of DeepStreaks is quantified by the performance on the test data sets as well as using known near-Earth objects observed by ZTF. The system is deployed and adapted for usage within the ZTF Solar-System framework and has significantly reduced human involvement in the streak identification process, from several hours to typically under 10 minutes per day.
Shreya Anand, Jennifer Barnes, Sheng Yang, Mansi M. Kasliwal, Michael W. Coughlin, Jesper Sollerman, Kishalay De, Christoffer Fremling, Alessandra Corsi, Anna Y. Q. Ho, Arvind Balasubramanian, Conor Omand, Gokul P. Srinivasaragavan, S. Bradley Cenko, Tomas Ahumada, Igor Andreoni, Aishwarya Dahiwale, Kaustav Kashyap Das, Jacob Jencson, Viraj Karambelkar, Harsh Kumar, Brian D. Metzger, Daniel Perley, Nikhil Sarin, Tassilo Schweyer, Steve Schulze, Yashvi Sharma, Tawny Sit, Robert Stein, Leonardo Tartaglia, Samaporn Tinyanont, Anastasios Tzanidakis, Jan van Roestel, Yuhan Yao, Joshua S. Bloom, David O. Cook, Richard Dekany, Matthew J. Graham, Steven L. Groom, David L. Kaplan, Frank J. Masci, Michael S. Medford, Reed Riddle, Chaoran Zhang
Feb 18, 2023·astro-ph.HE·PDF One of the open questions following the discovery of GW170817 is whether neutron star mergers are the only astrophysical sites capable of producing $r$-process elements. Simulations have shown that 0.01-0.1M$_\odot$ of $r$-process material could be generated in the outflows originating from the accretion disk surrounding the rapidly rotating black hole that forms as a remnant to both neutron star mergers and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature of $r$-process nucleosynthesis in the binary neutron star merger GW170817 was its long-lasting near-infrared emission, thus motivating a systematic photometric study of the light curves of broadlined stripped-envelope (Ic-BL) supernovae (SNe) associated with collapsars. We present the first systematic study of 25 SNe Ic-BL -- including 18 observed with the Zwicky Transient Facility and 7 from the literature -- in the optical/near-infrared bands to determine what quantity of $r$-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account for $r$-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on the $r$-process mass for these SNe. We also perform independent light curve fits to models without $r$-process. We find that the $r$-process-free models are a better fit to the light curves of the objects in our sample. Thus we find no compelling evidence of $r$-process enrichment in any of our objects. Further high-cadence infrared photometric studies and nebular spectroscopic analysis would be sensitive to smaller quantities of $r$-process ejecta mass or indicate whether all collapsars are completely devoid of $r$-process nucleosynthesis.
Thomas Kupfer, Evan B. Bauer, Kevin B. Burdge, Eric C. Bellm, Lars Bildsten, Jim Fuller, JJ Hermes, Shrinivas R. Kulkarni, Thomas A. Prince, Jan van Roestel, Richard Dekany, Dmitry A. Duev, Michael Feeney, Matteo Giomi, Matthew J. Graham, Stephen Kaye, Russ R. Laher, Frank J. Masci, Michael Porter, Reed Riddle, David L. Shupe, Roger M. Smith, Maayane T. Soumagnac, Paula Szkody, Charlotte Ward
Using high-cadence observations from the Zwicky Transient Facility at low Galactic latitudes, we have discovered a new class of pulsating, hot, compact stars. We have found four candidates, exhibiting blue colors ($g-r\leq-0.1$ mag), pulsation amplitudes of $>5\%$, and pulsation periods of $200 - 475$ sec. Fourier transforms of the lightcurves show only one dominant frequency. Phase-resolved spectroscopy for three objects reveals significant radial velocity, T$_{\rm eff}$ and log(g) variations over the pulsation cycle, consistent with large amplitude radial oscillations. The mean T$_{\rm eff}$ and log(g) for these stars are consistent with hot subdwarf B (sdB) effective temperatures and surface gravities. We calculate evolutionary tracks using MESA and adiabatic pulsations using GYRE for low-mass helium-core pre-white dwarfs and low mass helium-burning stars. Comparison of low-order radial oscillation mode periods with the observed pulsation periods show better agreement with the pre-white dwarf models. Therefore, we suggest that these new pulsators and Blue Large-Amplitude Pulsators (BLAPs) could be members of the same class of pulsators, composed of young $\approx0.25-0.35$ M$_\odot$ helium-core pre-white dwarfs.
Yuhan Yao, S. R. Kulkarni, Kevin B. Burdge, Ilaria Caiazzo, Kishalay De, Dillon Dong, C. Fremling, Mansi M. Kasliwal, Thomas Kupfer, Jan van Roestel, Jesper Sollerman, Ashot Bagdasaryan, Eric C. Bellm, S. Bradley Cenko, Andrew J. Drake, Dmitry A. Duev, Matthew J. Graham, Stephen Kaye, Frank J. Masci, Nicolas Miranda, Thomas A. Prince, Reed Riddle, Ben Rusholme, Maayane T. Soumagnac
Nov 30, 2020·astro-ph.HE·PDF AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234) is a transient first reported by the ATLAS optical survey in 2019 December. It rose to prominence upon detection, three months later, by the Spektrum-Roentgen-Gamma (SRG) mission in its first all-sky survey. X-ray observations reported in Yao et al. suggest that AT2019wey is a Galactic low-mass X-ray binary (LMXB) with a black hole (BH) or neutron star (NS) accretor. Here we present ultraviolet, optical, near-infrared, and radio observations of this object. We show that the companion is a short-period (P < 16 hr) low-mass (< 1 Msun) star. We consider AT2019wey to be a candidate BH system since its locations on the L_radio--L_X and L_opt--L_X diagrams are closer to BH binaries than NS binaries. We demonstrate that from 2020 June to August, despite the more than 10 times brightening at radio and X-ray wavelengths, the optical luminosity of AT2019wey only increased by 1.3--1.4 times. We interpret the UV/optical emission before the brightening as thermal emission from a truncated disk in a hot accretion flow and the UV/optical emission after the brightening as reprocessing of the X-ray emission in the outer accretion disk. AT2019wey demonstrates that combining current wide-field optical surveys and SRG provides a way to discover the emerging population of short-period BH LMXB systems with faint X-ray outbursts.
Eleni Tsaprazi, Jens Jasche, Ariel Goobar, Hiranya V. Peiris, Igor Andreoni, Michael W. Coughlin, Christoffer U. Fremling, Matthew J. Graham, Mansi Kasliwal, Shri R. Kulkarni, Ashish A. Mahabal, Reed Riddle, Jesper Sollerman, Anastasios Tzanidakis
The new generation of wide-field time-domain surveys has made it feasible to study the clustering of supernova (SN) host galaxies in the large-scale structure (LSS) for the first time. We investigate the LSS environment of SN populations, using 106 dark matter density realisations with a resolution of $\sim$ 3.8 Mpc, constrained by the 2M++ galaxy survey. We limit our analysis to redshift $z<0.036$, using samples of 498 thermonuclear and 782 core-collapse SNe from the Zwicky Transient Facility's Bright Transient Survey and Census of the Local Universe catalogues. We detect clustering of SNe with high significance; the observed clustering of the two SNe populations is consistent with each other. Further, the clustering of SN hosts is consistent with that of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey (BOSS) DR12 spectroscopic galaxy sample in the same redshift range. Using a tidal shear classifier, we classify the LSS into voids, sheets, filaments and knots. We find that both SNe and SDSS galaxies are predominantly found in sheets and filaments. SNe are significantly under-represented in voids and over-represented in knots compared to the volume fraction in these structures. This work opens the potential for using forthcoming wide-field deep SN surveys as a complementary LSS probe.
Anna Y. Q. Ho, Daniel A. Perley, Avishay Gal-Yam, Ragnhild Lunnan, Jesper Sollerman, Steve Schulze, Kaustav K. Das, Dougal Dobie, Yuhan Yao, Christoffer Fremling, Scott Adams, Shreya Anand, Igor Andreoni, Eric C. Bellm, Rachel J. Bruch, Kevin B. Burdge, Alberto J. Castro-Tirado, Aishwarya Dahiwale, Kishalay De, Richard Dekany, Andrew J. Drake, Dmitry A. Duev, Matthew J. Graham, George Helou, David L. Kaplan, Viraj Karambelkar, Mansi M. Kasliwal, Erik C. Kool, S. R. Kulkarni, Ashish A. Mahabal, Michael S. Medford, A. A. Miller, Jakob Nordin, Eran Ofek, Glen Petitpas, Reed Riddle, Yashvi Sharma, Roger Smith, Adam J. Stewart, Kirsty Taggart, Leonardo Tartaglia, Anastasios Tzanidakis, Jan Martin Winters
May 18, 2021·astro-ph.HE·PDF We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 d < t1/2 < 12 d, of which 28 have blue (g-r<-0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had high-S/N predominantly featureless spectra and luminous radio emission: AT2018lug and AT2020xnd. Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad H$α$ in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (six) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 22 of the transients. All X-ray and radio observations resulted in non-detections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs, and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.
Eunkyu Han, Philip S. Muirhead, Jonathan J. Swift, Christoph Baranec, Nicholas M. Law, Reed Riddle, Dani Atkinson, Gregory N. Mace, Daniel DeFelippis
Jul 21, 2017·astro-ph.SR·PDF Several low-mass eclipsing binary stars show larger than expected radii for their measured mass, metallicity and age. One proposed mechanism for this radius inflation involves inhibited internal convection and starspots caused by strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has proven confounding to this scenario. \citet{Cakirli2013a} measured a radius for the secondary component that is twice as large as model predictions for stars with the same mass and age, but a primary mass that is consistent with predictions. \citet[][]{Iglesias2017} independently measured the radii and masses of the component stars and found that the radius of the secondary is not in fact inflated with respect to models, but that the primary is, consistent with the inhibited convection scenario. However, in their mass determinations, \citet[][]{Iglesias2017} lacked independent radial velocity measurements for the secondary component due to the star's faintness at optical wavelengths. The secondary component is especially interesting as its purported mass is near the transition from partially-convective to a fully-convective interior. In this article we independently determined the masses and radii of the component stars of T-Cyg1-12664 using archival {\it Kepler} data and radial velocity measurements of both component stars obtained with IGRINS on the Discovery Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that neither of the component stars is inflated with respect to models. Our results are broadly consistent with modern stellar evolutionary models for main-sequence M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.
Carl Ziegler, Nicholas M. Law, Christoph Baranec, Tim Morton, Reed Riddle, Dani Atkinson, Larissa Nofi
The Robo-AO Kepler Planetary Candidate Survey is observing every Kepler planet candidate host star (KOI) with laser adaptive optics imaging to hunt for blended nearby stars which may be physically associated companions. With the unparalleled efficiency provided by the first fully robotic adaptive optics system, we perform the critical search for nearby stars (0.15" to 4.0" separation with contrasts up to 6 magnitudes) that dilute the observed planetary transit signal, contributing to inaccurate planetary characteristics or astrophysical false positives. We present 3313 high resolution observations of Kepler planetary hosts from 2012-2015, discovering 479 nearby stars. We measure an overall nearby star probability rate of 14.5\pm0.8%. With this large data set, we are uniquely able to explore broad correlations between multiple star systems and the properties of the planets which they host, providing insight into the formation and evolution of planetary systems in our galaxy. Several KOIs of particular interest will be discussed, including possible quadruple star systems hosting planets and updated properties for possible rocky planets orbiting with in their star's habitable zone.
Christoph Baranec, Carl Ziegler, Nicholas M. Law, Tim Morton, Reed Riddle, Dani Atkinson, Jessica Schonhut, Justin Crepp
Apr 28, 2016·astro-ph.EP·PDF We initiated the Robo-AO Kepler Planetary Candidate Survey in 2012 to observe each Kepler exoplanet candidate host star with high-angular-resolution visible-light laser-adaptive-optics imaging. Our goal is to find nearby stars lying in Kepler's photometric apertures that are responsible for the relatively high probability of false-positive exoplanet detections and that cause underestimates of the size of transit radii. Our comprehensive survey will also shed light on the effects of stellar multiplicity on exoplanet properties and will identify rare exoplanetary architectures. In this second part of our ongoing survey, we observed an additional 969 Kepler planet candidate hosts and we report blended stellar companions up to $Δm \approx 6$ that contribute to Kepler's measured light curves. We found 203 companions within $\sim$4" of 181 of the Kepler stars, of which 141 are new discoveries. We measure the nearby-star probability for this sample of Kepler planet candidate host stars to be 10.6% $\pm$ 1.1% at angular separations up to 2.5", significantly higher than the 7.4% $\pm$ 1.0% probability discovered in our initial sample of 715 stars; we find the probability increases to 17.6% $\pm$ 1.5% out to a separation of 4.0". The median position of KOIs observed in this survey are 1.1$^{\circ}$ closer to the galactic plane which may account for some of the nearby-star probability enhancement. We additionally detail 50 Keck adaptive optics images of Robo-AO observed KOIs in order to confirm 37 companions detected at a $<5σ$ significance level and to obtain additional infrared photometry on higher-significance detected companions.
Carl Ziegler, Nicholas M. Law, Christoph Baranec, Ward Howard, Tim Morton, Reed Riddle, Dmitry A. Duev, Maïssa Salama, Rebecca Jensen-Clem, S. R. Kulkarni
Apr 26, 2018·astro-ph.EP·PDF The Kepler light curves used to detect thousands of planetary candidates are susceptible to dilution due to blending with previously unknown nearby stars. With the automated laser adaptive optics instrument, Robo-AO, we have observed 620 nearby stars around 3857 planetary candidates host stars. Many of the nearby stars, however, are not bound to the KOI. In this paper, we quantify the association probability between each KOI and detected nearby stars through several methods. Galactic stellar models and the observed stellar density are used to estimate the number and properties of unbound stars. We estimate the spectral type and distance to 145 KOIs with nearby stars using multi-band observations from Robo-AO and Keck-AO. We find most nearby stars within 1" of a Kepler planetary candidate are likely bound, in agreement with past studies. We use likely bound stars as well as the precise stellar parameters from the California Kepler Survey to search for correlations between stellar binarity and planetary properties. No significant difference between the binarity fraction of single and multiple planet systems is found, and planet hosting stars follow similar binarity trends as field stars, many of which likely host their own non-aligned planets. We find that hot Jupiters are ~4x more likely than other planets to reside in a binary star system. We correct the radius estimates of the planet candidates in characterized systems and find that for likely bound systems, the estimated planetary candidate radii will increase on average by a factor of 1.77, if either star is equally likely to host the planet. We find that the planetary radius gap is robust to the impact of dilution, and find an intriguing 95%-confidence discrepancy between the radius distribution of small planets in single and binary systems.
Carl Ziegler, Nicholas M. Law, Christoph Baranec, Tim Morton, Reed Riddle, Nathan De Lee, Daniel Huber, Suvrath Mahadevan, Joshua Pepper
Jun 26, 2018·astro-ph.EP·PDF We use the Robo-AO survey of Kepler planetary candidate host stars, the largest adaptive optics survey yet performed, to measure the recovery rate of close stellar binaries in Gaia DR2. We find that Gaia recovers binaries down to 1" at magnitude contrasts as large as 6; closer systems are not resolved, regardless of secondary brightness. Gaia DR2 binary detection does not have a strong dependence on the orientation of the stellar pairs. We find 177 nearby stars to Kepler planetary candidate host stars in Gaia DR2 that were not detected in the Robo-AO survey, almost all of which are faint (G>20); the remainder were largely targets observed by Robo-AO in poor conditions. If the primary star is the host, the impact on the radii estimates of planet candidates in these systems is likely minimal; many of these faint stars, however, could be faint eclipsing binaries that are the source of a false positive planetary transit signal. With Robo-AO and Gaia combined, we find that 18.7% of Kepler planet candidate hosts have nearby stars within 4". We also find 36 nearby stars in Gaia DR2 around 35 planetary candidate host stars detected with K2. The nearby star fraction rate for K2 planetary candidates is significantly lower than that for the primary Kepler mission. The binary recovery rate of Gaia will improve initial radius estimates of future TESS planet candidates significantly, however ground-based high-resolution follow-up observations are still needed for precise characterization and confirmation. The sensitivity of Gaia to closely separated binaries is expected to improve in later data releases.