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The tidal forces of a black hole can rip apart a star that passes too close to it, resulting in a stellar Tidal Disruption Event (TDE, (1)). In some such encounters, the black hole can launch a powerful relativistic jet (2-6). If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic TDEs have the potential to unveil cosmological (redshift z>1) quiescent black holes and are ideal test beds to understand the radiative mechanisms operating in super-Eddington jets. Here, we present multi-wavelength (X-ray, UV, optical, and radio) observations of the optically discovered transient AT 2022cmc at z=1.193 (7). Its unusual X-ray properties, including a peak observed luminosity of >1048 erg s-1, systematic variability on timescales as short as 1000 seconds, and overall duration lasting more than 30 days in the rest-frame are traits associated with relativistic TDEs. This makes AT 2022cmc only the fourth member of this rare class and the first one identified in the optical and with well-sampled optical data. The X-ray to radio spectral energy distributions spanning 5-50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays), and thermal emission similar to that seen in low-redshift TDEs (UV/optical). Our modeling implies a beamed, highly relativistic jet akin to blazars (e.g., (8,9)) but requires extreme matter-domination, i.e, high ratio of electron-to-magnetic field energy densities in the jet, and challenges our theoretical understanding of jets. This work provides one of the best multi-wavelength datasets of a newborn relativistic jet to date and will be invaluable for testing more sophisticated jet models, and for identifying more such events in transient surveys.

The aim of this work is to evaluate the performance of photometric metallicity [Fe/H], determined based on V-band light-curves photometrically transformed from the gr-band light-curves. We tested this by using a set of homogeneous sample of fundamental mode RR Lyrae located in the Kepler field. It was found that the color-term is necessary in such photometric transformation. We demonstrated that including the color-term the determined photometric [Fe/H] are in good agreement to the spectroscopic [Fe/H], either based on the calibrated or the transformed V-band light-curves. We also tested the impact of Blazhko RR Lyrae in determining the photometric Fe/H], and found that Blazhko RR Lyrae can give consistent photometric [Fe/H]. Finally, we derived independent gVr-band [Fe/H]-$\phi_{31}$-P relations (where $\phi_{31}$ and P are Fourier parameter and pulsation period, respectively) using our light-curves. The V-band relation is in good agreement with the most recent determination given in the literature., Comment: 12 pages, 2 Tables and 7 Figures; AJ accepted

The transiting planet HD80606b undergoes a 1000-fold increase in insolation during its 111-day orbit due to it being highly eccentric (e=0.93). The planet's effective temperature increases from 400K to over 1400K in a few hours as it makes a rapid passage to within 0.03AU of its host star during periapsis. Spectroscopic observations during the eclipse (which is conveniently oriented a few hours before periapsis) of HD80606b with the James Webb Space Telescope (JWST) are poised to exploit this highly variable environment to study a wide variety of atmospheric properties, including composition, chemical and dynamical timescales, and large scale atmospheric motions. Critical to planning and interpreting these observations is an accurate knowledge of the planet's orbit. We report on observations of two full-transit events: 7 February 2020 as observed by the TESS spacecraft and 7--8 December 2021 as observed with a worldwide network of small telescopes. We also report new radial velocity observations which when analyzed with a coupled model to the transits greatly improve the planet's orbital ephemeris. Our new orbit solution reduces the uncertainty in the transit and eclipse timing of the JWST era from tens of minutes to a few minutes. When combined with the planned JWST observations, this new precision may be adequate to look for non-Keplerian effects in the orbit of HD80606b., Comment: Accepted for publication in AJ; in press

Mira variables are asymptotic giant-branch pulsating stars with long pulsation periods and large amplitudes in optical bands. By applying the random forest algorithm to the I-band light curves for the Miras in the Magellanic Clouds, we have classified these Miras into regular Miras and nonregular Miras. Nonregular Miras exhibit a long-term variation in addition to their primary pulsation periods. Our results confirm that the period–luminosity relation for maximum light has a small dispersion, but only occurs on the regular oxygen-rich Miras, which we recommend to be applied in future distance-scale work. We have also collected multiband photometry for these Miras to perform a spectral energy distribution fitting with stellar and dust components, showing that a significant fraction of dust is present around the nonregular Miras. According to our results, we believe that the periodic long-term variations seen in the nonregular Miras might be due to the presence of dust.

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., 28 pages, 7 Tables and 24 Figures. AJ accepted

In this work, we aimed to derive the $gri$-band period-luminosity (PL) and period-luminosity-color (PLC) relations for late-type contact binaries, for the first time, located in the globular clusters, using the homogeneous light curves collected by the Zwicky Transient Factory (ZTF). We started with 79 contact binaries in 15 globular clusters, and retained 30 contact binaries in 10 globular clusters that have adequate number of data points in the ZTF light curves and unaffected by blending. Magnitudes at mean and maximum light of these contact binaries were determined using a fourth-order Fourier expansion, while extinction corrections were done using the {\tt Bayerstar2019} 3D reddening map together with adopting the homogeneous distances to their host globular clusters. After removing early-type and "anomaly" contact binaries, our derived $gri$-band PL and period-Wesenheit (PW) relations exhibit a much larger dispersion with large errors on the fitted coefficients. Nevertheless, the $gr$-band PL and PW relations based on this small sample of contact binaries in globular clusters were consistent with those based on a larger sample of nearby contact binaries. Good agreements of the PL and PW relations suggested both samples of contact binaries in the local Solar neighborhood and in the distant globular clusters can be combined and used to derive and calibrate the PL, PW and PLC relations. The final derived $gr$-band PL, PW and PLC relations were much improved than those based on the limited sample of contact binaries in the globular clusters., 26 pages, 4 Tables and 16 Figures; AJ Accepted

We present low-resolution spectra collected with the Spectral Energy Distribution Machine (SEDM) for an IW And-type dwarf nova, HO Puppis, and a Be star, V722 Tauri. The SEDM is an integrated field unit spectrograph mounted on the 60 inch telescope at the Palomar Observatory, with a spectral resolution of R ∼ 100 in the optical wavelength range. The Hα emission line was clearly detected for the bright Be star V722 Tauri at ∼12.5 mag, but barely detected in the spectra for the ∼13.7 mag HO Puppis. Our SEDM observations could be used as guidance for observing similar objects with the SEDM, as well as other R ∼ 100 spectrographs, in the future.

We present the first absolute calibration for the yellow post-asymptotic-giant-branch (PAGB) stars in the g- and r-band based on time-series observations from the Zwicky Transient Facility. These absolute magnitudes were calibrated using four yellow PAGB stars (one non-varying star and three Type II Cepheids) located in the globular clusters. We provide two calibrations of the gr-band absolute magnitudes for the yellow PAGB stars, by using an arithmetic mean and a linear regression. We demonstrate that the linear regression provides a better fit to the g-band absolute magnitudes for the yellow PAGB stars. These calibrated gr-band absolute magnitudes have a potential to be used as population II distance indicators in the era of time-domain synoptic sky surveys., 6 pages, 3 Figures and 1 Table; AJ accepted

We present the first gri-band period-luminosity (PL) and period-Wesenheit (PW) relations for 37 Type II Cepheids (hereafter TIIC) located in 18 globular clusters based on photometric data from the Zwicky Transient Facility. We also updated BV IJHK-band absolute magnitudes for 58 TIIC in 24 globular clusters using the latest homogeneous distances to the globular clusters. The slopes of g/r/i and B/V/I band PL relations are found to be statistically consistent when using the same sample of distance and reddening. We employed the calibration of ri-band PL/PW relations in globular clusters to estimate a distance to M31 based on a sample of ~270 TIIC from the PAndromeda project. The distance modulus to M31, obtained using calibrated ri-band PW relation, agrees well with the recent determination based on classical Cepheids. However, distance moduli derived using the calibrated r- and i-band PL relations are systematically smaller by ~0.2 mag, suggesting there are possible additional systematic error on the PL relations. Finally, we also derive the period-color (PC) relations and for the first time the period-Q-index (PQ) relations, where the Q-index is reddening-free, for our sample of TIIC. The PC relations based on (r-i) and near-infrared colors and the PQ relations are found to be relatively independent of the pulsation periods., Comment: 14 pages, 8 Figures and 5 Tables, AJ accepted

Nova eruptions, thermonuclear explosions on the surfaces of white dwarfs (WDs), are now recognized to be among the most common shock-powered astrophysical transients. We present the early discovery and rapid ultraviolet (UV), optical, and infrared (IR) temporal development of AT 2019qyl, a recent nova in the nearby Sculptor Group galaxy NGC 300. The light curve shows a rapid rise lasting $\lesssim 1$ day, reaching a peak absolute magnitude of $M_V = -9.2$ mag, and a very fast decline, fading by 2 mag over 3.5 days. A steep dropoff in the light curves after 71 days and the rapid decline timescale suggest a low-mass ejection from a massive WD with $M_{\rm WD} \gtrsim 1.2~M_{\odot}$. We present an unprecedented view of the early spectroscopic evolution of such an event. Three spectra prior to the peak reveal a complex, multicomponent outflow giving rise to internal collisions and shocks in the ejecta of an He/N-class nova. We identify a coincident IR-variable counterpart in the extensive preeruption coverage of the transient location and infer the presence of a symbiotic progenitor system with an O-rich asymptotic-giant-branch donor star, as well as evidence for an earlier UV-bright outburst in 2014. We suggest that AT 2019qyl is analogous to the subset of Galactic recurrent novae with red-giant companions such as RS Oph and other embedded nova systems like V407 Cyg. Our observations provide new evidence that internal shocks between multiple, distinct outflow components likely contribute to the generation of the shock-powered emission from such systems., 32 pages, 10 figures, accepted in ApJ

We observed Episodically Active Asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and have found that it is no longer active after its recent outbursts at the end of 2018 and start of 2019. The inactivity during this apparation allowed us to measure the absolute magnitude of Gault of H_r = 14.63 +/- 0.02, G_r = 0.21 +/- 0.02 from our secular phasecurve observations. In addition, we were able to constrain Gault's rotation period using time-series photometric lightcurves taken over 17 hours on multiple days in 2020 August, September and October. The photometric lightcurves have a repeating $\lesssim$0.05 magnitude feature suggesting that (6478) Gault has a rotation period of ~2.5 hours and may have a semi-spherical or top-like shape, much like Near-Earth Asteroids Ryugu and Bennu. The rotation period of ~2.5 hours is near to the expected critical rotation period for an asteroid with the physical properties of (6478) Gault suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spun up by the Yarkovsky-O'Keefe-Radzievskii-Paddack effect., Comment: 23 pages, 18 figures; Accepted by ApJ Letters

Full list of authors: Plachy, E.; Pál, A.; Bódi, A.; Szabó, P.; Molnár, L.; Szabados, L.; Benkő, J. M.; Anderson, R. I.; Bellinger, E. P.; Bhardwaj, A.; Ebadi, M.; Gazeas, K.; Hambsch, F. -J.; Hasanzadeh, A.; Jurkovic, M. I.; Kalaee, M. J.; Kervella, P.; Kolenberg, K.; Mikołajczyk, P.; Nardetto, N. Nemec, J. M.; Netzel, H.; Ngeow, C. -C.; Ozuyar, D.; Pascual-Granado, J.; Pilecki, B.; Ripepi, V.; Skarka, M.; Smolec, R.; Sódor, Á.; Szabó, R.; Christensen-Dalsgaard, J.; Jenkins, J. M.; Kjeldsen, H.; Ricker, G. R.; Vanderspek, R., We present the first analysis of Cepheid stars observed by the TESS space mission in Sectors 1–5. Our sample consists of 25 pulsators: ten fundamental mode, three overtone and two double-mode classical Cepheids, plus three type II and seven anomalous Cepheids. The targets were chosen from fields with different stellar densities, both from the Galactic field and from the Magellanic System. Three targets have 2 minutes cadence light curves available by the TESS Science Processing Operations Center: for the rest, we prepared custom light curves from the full-frame images with our own differential photometric FITSH pipeline. Our main goal was to explore the potential and the limitations of TESS concerning the various subtypes of Cepheids. We detected many low-amplitude features: weak modulation, period jitter, and timing variations due to light-time effect. We also report signs of nonradial modes and the first discovery of such a mode in an anomalous Cepheid, the overtone star XZ Cet, which we then confirmed with ground-based multicolor photometric measurements. We prepared a custom photometric solution to minimize saturation effects in the bright fundamental-mode classical Cepheid, β Dor with the lightkurve software, and we revealed strong evidence of cycle-to-cycle variations in the star. In several cases, however, fluctuations in the pulsation could not be distinguished from instrumental effects, such as contamination from nearby sources, which also varies between sectors. Finally, we discuss how precise light-curve shapes will be crucial not only for classification purposes but also to determine physical properties of these stars. © 2021. The American Astronomical Society. All rights reserved., The research leading to these results has been supported by the Hungarian National Research, Development and Innovation Office (NKFIH) grants KH_18 130405, K-125015, GINOP 2.3.2-15-2016-00033, and NN-129075, and the Lendulet LP2014-17 and LP2018-7/2020 grants of the Hungarian Academy of Sciences (HAS). The work reported on in this publication has been supported by the MW-Gaia COST Action (CA18104). Partial funding of the computational infrastructure and database servers were received from the grant KEP-7/2018 of the HAS. E.P. was supported by the Janos Bolyai Research Scholarship of the HAS. L.M. was supported by the Premium Postdoctoral Research Program of the HAS. C.C.N. thanks the funding from Ministry of Science and Technology (Taiwan) under the contract 107-2119-M-008014-MY2. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (grant agreement No. DNRF106). R.Sm. was supported by the National Science Center, Poland, Sonata BIS project 2018/30/E/ST9/00598. M.I.J. was supported by the Ministry of Education, Science and Technological Development (contract number 451-03-68/2020-14/200002) of Republic of Serbia. A.B. acknowledges a Gruber fellowship 2020 grant sponsored by the Gruber Foundation and the International Astronomical Union and is supported by the EACOA Fellowship Program under the umbrella of the East Asia Core Observatories Association, which consists of the Academia Sinica Institute of Astronomy and Astrophysics, the National Astronomical Observatory of Japan, the Korea Astronomy and Space Science Institute, and the National Astronomical Observatories of the Chinese Academy of Sciences. J.P.G. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and from Spanish public funds for research under project ESP2017-87676-C5-5-R. P.M. acknowledges support from the NCN grant No. 2016/21/B/ST9/01126. M.S. acknowledges the financial support of the Operational Program Research, Development and Education-Project Postdoc@MUNI(No.CZ.02.2.69/0.0/0.0/16_027/0008360) and the MSMT Inter Transfer program LTT20015. P.K. and N.N. acknowledge the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-15-CE31-0012-01 (project UnlockCepheids). The research leading to these results has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 695099). This work has made use of data from the European Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, http://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by NASAs Science Mission directorate. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products.

We present time-resolved visible spectrophotometry of 2020 CD₃, the second known minimoon. The spectrophotometry was taken with the Keck I/Low Resolution Imaging Spectrometer between wavelengths 434 and 912 nm in the B, g, V, R, I, and RG850 filters as it was leaving the Earth–Moon system on 2020 March 23 UTC. The spectrum of 2020 CD₃ resembles V-type asteroids and some lunar rock samples with a 434–761 nm reddish slope of ~18%/100 nm (g–r = 0.62 ± 0.08 and r–i = 0.21 ± 0.06) with an absorption band at ~900 nm corresponding to i–z = −0.54 ± 0.10. Combining our measured H of 31.9 ± 0.1 with an albedo of 0.35 typical for V-type asteroids, we determine 2020 CD₃'s diameter to be ~0.9 ± 0.1 m, making it the first minimoon and one of the smallest asteroids to be spectrally studied. We use our time-series photometry to detect significant periodic light-curve variations with a period of ~573 s and amplitude of ~1. In addition, we extend the observational arc of 2020 CD₃ to 37 days, to 2020 March 23 UTC. From the improved orbital solution for 2020 CD₃, we estimate the likely duration of its capture to be ~2 yr and the nongravitational perturbation on its orbit due to radiation pressure with an area-to-mass ratio of (6.9 ± 2.4) × 10⁻⁴ m² kg⁻¹ implying a density of 2.3 ± 0.8 g cm⁻³, broadly compatible with other meter-scale asteroids and lunar rock. We searched for prediscovery detections of 2020 CD₃ in the Zwicky Transient Facility archive as far back as 2018 October but were unable to locate any positive detections.

We present new near-infrared ($JHK_s$) time-series observations of RR Lyrae variables in the Messier 3 (NGC 5272) globular cluster using the WIRCam instrument at the 3.6-m Canada France Hawaii Telescope. Our observations cover a sky area of $\sim 21'\times 21'$ around the cluster center and provide an average of twenty epochs of homogeneous $JHK_s$-band photometry. New homogeneous photometry is used to estimate robust mean magnitudes for 175 fundamental-mode (RRab), 47 overtone-mode (RRc), and 11 mixed-mode (RRd) variables. Our sample of 233 RR Lyrae variables is the largest thus far obtained in a single cluster with time-resolved, multi-band near-infrared photometry. Near-infrared to optical amplitude ratios for RR Lyrae in Messier 3 exhibit a systematic increase moving from RRc to short-period ($P < 0.6$~days) and long-period ($P \gtrsim 0.6$~days) RRab variables. We derive $JHK_s$-band Period--Luminosity relations for RRab, RRc, and the combined sample of variables. Absolute calibrations based on the theoretically predicted Period--Luminosity--Metallicity relations for RR Lyrae stars yield a distance modulus, $��= 15.041 \pm 0.017~(\textrm{statistical}) \pm 0.036~(\textrm{systematic})$~mag, to Messier 3. When anchored to trigonometric parallaxes for nearby RR Lyrae stars from the {\it Hubble Space Telescope} and the {\it Gaia} mission, our distance estimates are consistent with those resulting from the theoretical calibrations, albeit with relatively larger systematic uncertainties., 22 pages, 14 figures, Accepted for publication in The Astronomical Journal

Two high-cadence surveys aiming for rotation period measurements of asteroids have been conducted in 2019 January and October using the Zwicky Transient Facility. From the surveys, 25 large superfast rotators (SFRs) were discovered and they are all main-belt asteroids (MBAs), except for one Mars crosser. These large SFRs have a diameter ranging from 0.43 to 7.87 km and a rotation period between 0.48 and 1.95 hr. Considering their diameters and fast rotations, they cannot be explained by rubble-pile structure unless using extraordinary high bulk densities. Cohesion, if available, can conserve these large SFRs. The estimated cohesion for these large SFRs could be up to thousands of pascals, much higher than the currently estimated cohesion for asteroids and that generated by the regolith of Moon and Mars. Such high-level cohesion can be produced from fine-grain regolith, like clay. However, the availability of such fine-grain regolith for asteroids is still unknown. Although the possibility of these large SFRs being large monolithic objects cannot be ruled out, this scenario is very unlikely given that the timescale of disruptive impact for MBAs in a similar diameter range is 107–108 yr.

We measured the parallax of the James Webb Space Telescope based on near simultaneous observations using the Lulin One-meter Telescope and the GROWTH India Telescope, separated at a distance of ~4214 km. This serves a great demonstration for the concept of parallax commonly taught in introductory astronomy courses., 2 pages and 1 figure, RNAAS in-press

This paper is the eighth in a series presenting the results of the dynamical analysis of velocity fields of Galactic objects on the assumption that the system is subject to moderately unstable, low-amplitude, tightly wound, and rigidly rotating Lin–Shu density waves. The data of 61 masers associated with star-forming regions having distances d

Near-Earth Objects (NEOs) that orbit the Sun on or within Earth's orbit are tricky to detect for Earth-based observers due to their proximity to the Sun in the sky. These small bodies hold clues to the dynamical history of the inner solar system as well as the physical evolution of planetesimals in extreme environments. Populations in this region include the Atira and Vatira asteroids, as well as Venus and Earth co-orbital asteroids. Here we present a twilight search for these small bodies, conducted using the 1.2-m Oschin Schmidt and the Zwicky Transient Facility (ZTF) camera at Palomar Observatory. The ZTF twilight survey operates at solar elongations down to $35^\circ$ with limiting magnitude of $r=19.5$. During a total of 40 evening sessions and 62 morning sessions conducted between 2018 November 15 and 2019 June 23, we detected 6 Atiras, including 2 new discoveries 2019 AQ$_3$ and 2019 LF$_6$, but no Vatiras or Earth/Venus co-orbital asteroids. NEO population models show that these new discoveries are likely only the tip of the iceberg, with the bulk of the population yet to be found. The population models also suggest that we have only detected 5--$7\%$ of the $H, AJ accepted

All authors: Kasliwal, Mansi M.; Anand, Shreya; Ahumada, Tomás; Stein, Robert; Carracedo, Ana Sagués; Andreoni, Igor; Coughlin, Michael W.; Singer, Leo P.; Kool, Erik C.; De, Kishalay; Kumar, Harsh; AlMualla, Mouza; Yao, Yuhan; Bulla, Mattia; Dobie, Dougal; Reusch, Simeon; Perley, Daniel A.; Cenko, S. Bradley; Bhalerao, Varun; Kaplan, David L.; Sollerman, Jesper; Goobar, Ariel; Copperwheat, Christopher M.; Bellm, Eric C.; Anupama, G. C.; Corsi, Alessandra; Nissanke, Samaya; Agudo, Iván; Bagdasaryan, Ashot; Barway, Sudhanshu; Belicki, Justin; Bloom, Joshua S.; Bolin, Bryce; Buckley, David A. H.; Burdge, Kevin B.; Burruss, Rick; Caballero-García, Maria D.; Cannella, Chris; Castro-Tirado, Alberto J.; Cook, David O.; Cooke, Jeff; Cunningham, Virginia; Dahiwale, Aishwarya; Deshmukh, Kunal; Dichiara, Simone; Duev, Dmitry A.; Dutta, Anirban; Feeney, Michael; Franckowiak, Anna; Frederick, Sara; Fremling, Christoffer; Gal-Yam, Avishay; Gatkine, Pradip; Ghosh, Shaon; Goldstein, Daniel A.; Golkhou, V. Zach; Graham, Matthew J.; Graham, Melissa L.; Hankins, Matthew J.; Helou, George; Hu, Youdong; Ip, Wing-Huen; Jaodand, Amruta; Karambelkar, Viraj; Kong, Albert K. H.; Kowalski, Marek; Khandagale, Maitreya; Kulkarni, S. R.; Kumar, Brajesh; Laher, Russ R.; Li, K. L.; Mahabal, Ashish; Masci, Frank J.; Miller, Adam A.; Mogotsi, Moses; Mohite, Siddharth; Mooley, Kunal; Mroz, Przemek; Newman, Jeffrey A.; Ngeow, Chow-Choong; Oates, Samantha R.; Patil, Atharva Sunil; Pandey, Shashi B.; Pavana, M.; Pian, Elena; Riddle, Reed; Sánchez-Ramírez, Rubén; Sharma, Yashvi; Singh, Avinash; Smith, Roger; Soumagnac, Maayane T.; Taggart, Kirsty; Tan, Hanjie; Tzanidakis, Anastasios; Troja, Eleonora; Valeev, Azamat F.; Walters, Richard; Waratkar, Gaurav; Webb, Sara; Yu, Po-Chieh; Zhang, Bin-Bin; Zhou, Rongpu; Zolkower, Jeffry, We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg2, a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10-25 yr-1. The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (-16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than-16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day-1 (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than-16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than 10-4, or φ > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of-16 mag would constrain the maximum fraction of bright kilonovae to, This work was supported by the Global Relay of Observatories Watching Transients Happen (GROWTH) project, funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among the California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. The ZTF forced photometry service was funded under Heising-Simons Foundation grant No. 12540303 (PI: Graham). The SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. The GROWTH-India telescope is a 70 cm telescope with a 0.7 degrees field of view, set up by the Indian Institute of Astrophysics and the Indian Institute of Technology Bombay with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India (https://sites.google.com/view/growthindia/). It is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). The GROWTH-India project is supported by SERB and administered by IUSSTF under grant No. IUSSTF/PIRE Program/GROWTH/2015-16. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi: 10.26093/cds/vizier). The original description of the VizieR service was published in A&AS 143, 23. These results made use of the Lowell Discovery Telescope (LDT) at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The Large Monolithic Imager was built by Lowell Observatory using funds provided by the National Science Foundation (AST-1005313). The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale and a grant from the Mt. Cuba Astronomical Foundation. The KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1 m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council, and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Some spectroscopic observations were obtained with the Southern African Large Telescope (SALT). The Photometric Redshifts for the Legacy Surveys (PRLS) catalog used in this paper was produced thanks to funding from the U.S. Department of Energy Office of Science, Office of High Energy Physics, via grant DE-SC0007914. This publication has made use of data collected at Lulin Observatory, partly supported by MoST grant 108-2112-M-008-001. Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias on the island of La Palma. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. A.G. and J.S. acknowledge support from the Knut and Alice Wallenberg Foundation and GREAT research environment grant 2016-06012, funded by the Swedish Research Council. Some of the work by D.A.P. was performed at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. D.A.P. was partially supported by a grant from the Simons Foundation. H.K. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. This work has been supported by the Spanish Science Ministry Centro de Excelencia Severo Ochoa Program under grant SEV-2017-0709. A.J.C.T. acknowledges support from the Junta de Andalucia (Project P07-TIC-03094) and Spanish Ministry Projects AYA2012-39727-C03-01, AYA2015-71718R, and PID-019-109974RB-I00. V.A.F. was supported by grant RFBR 19-02-00432. I.A. acknowledges support by a Ramon y Cajal grant (RYC-2013-14511) of the Ministerio de Ciencia, Innovacion, y Universidades (MICIU) of Spain. He also acknowledges financial support from MCIU through grant AYA2016-80889-P. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). A.C. acknowledges support from the National Science Foundation with grant No. 1907975. W.-H.I., A. K., K.-L.L., C.-C.N., A.P., H.T., and P.-C.Y. acknowledge support from Ministry of Science and Technology (MoST) Taiwan grants 104-2923-M-008-004-MY5, 107-2119-M-008-012, 108-2628-M-007-005-RSP, and 108-2112-M-007-025-MY3. D.D. is supported by an Australian Government Research Training Program Scholarship. S.A. is supported by the GROWTH project, funded by the National Science Foundation under PIRE grant No. 1545949. A.S.C. is supported by GREAT research environment grant 2016-06012, funded by the Swedish Research Council. E.C.K. acknowledges support from the G.R.E.A.T. research environment and the Wenner-Gren Foundations. A.J.C.T. is thankful for fruitful discussions with J. Cepa, E. Fernandez-Garcia, J. A. Font, S. Jeong, A. Martin-Carrillo, A. M. Sintes, and S. Sokolov. D.A.H.B. acknowledges research support from the National Research Foundation of South Africa. S.B.P. and V.B. acknowledge BRICS grant No. "DST/IMRCD/BRICS/PilotCall1/ProFCheap/2017(G)" for part of the present work. J.S.B. was partially supported by a Gordon and Betty Moore Foundation Data-Driven Discovery grant and a grant from the National Science Foundation, "Conceptualization of a Scalable Cyberinfrastructure Center for Multimessenger Astrophysics."

The Zwicky Transient Facility (ZTF) is a modern-day wide-field optical survey to systematically explore the transient and variable sky. The ZTF utilizes the 48-inch Samuel Oschin Schmidt Telescope located at the Palomar Observatory. This telescope is equipped with a mosaic CCD camera that provides a field of view of 47 squared degrees. The allocated observing time of ZTF can be divided into partnership time (40%), public time (40%) and Caltech time (20%). The public time contains two surveys: a 3-day cadence for the Northern Sky Survey and a 1-day cadence for the Galactic Plane Survey. Astronomical communities in South East Asian countries are encouraged to explore the public ZTF data once it is released in March 2019. Taiwan’s National Central University (NCU) is one of the partnered institutions, and a major ZTF-related project carried out at NCU is the ZTF Be stars variability (ZTF-BeV) program. The main goal of our program is to study the variability of Be stars in the range of ∼13.5 to ∼20.5 magnitudes.

We describe ZStreak, a semi-real-time pipeline specialized in detecting small, fast-moving near-Earth asteroids (NEAs) that is currently operating on the data from the newly-commissioned Zwicky Transient Facility (ZTF) survey. Based on a prototype originally developed by Waszczak et al. (2017) for the Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an improved machine-learning model that can cope with the $10\times$ data rate increment between PTF and ZTF. Since its first discovery on 2018 February 5 (2018 CL), ZTF/ZStreak has discovered $45$ confirmed new NEAs over a total of 232 observable nights until 2018 December 31. Most of the discoveries are small NEAs, with diameters less than $\sim100$ m. By analyzing the discovery circumstances, we find that objects having the first to last detection time interval under 2 hr are at risk of being lost. We will further improve real-time follow-up capabilities, and work on suppressing false positives using deep learning., PASP in press

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., Comment: 24 pages, 7 tables and 12 figures; ApJ accepted

We present new near-infrared, $JHK_s$, Period--Luminosity relations (PLRs) for RR Lyrae variables in the Messier 53 (M53 or NGC 5024) globular cluster. Multi-epoch $JHK_s$ observations, obtained with the WIRCam instrument on the 3.6-m Canada France Hawaii Telescope, are used for the first time to estimate precise mean-magnitudes for 63 RR Lyrae stars in M53 including 29 fundamental-mode (RRab) and 34 first-overtone modes (RRc) variables. The $JHK_s$-band PLRs for RR Lyrae stars are best constrained for RRab types with a minimal scatter of 22, 23, and 19 mmag, respectively. The combined sample of RR Lyrae is used to derive the $K_s$-band PLR, $K_s = -2.303 (0.063) \log P + 15.212 (0.016)$ exhibiting a $1\sigma$ dispersion of only $0.027$ mag. Theoretical Period--Luminosity--Metallicity (PLZ) relations are used to predict parallaxes for 400 Galactic RR Lyrae resulting in a median parallax zero-point offset of $-7\pm3~\mu$as in {\it Gaia} Early Data Release 3 (EDR3), which increases to $22\pm2~\mu$as if the parallax corrections are applied. We also estimate a robust distance modulus, $\mu_\textrm{M53} = 16.403 \pm 0.024$ (statistical) $\pm 0.033$ (systematic) mag, to M53 based on theoretical calibrations. Homogeneous and precise mean-magnitudes for RR Lyrae in M53 together with similar literature data for M3, M4, M5, and $\omega$ Cen are used to empirically calibrate a new RR Lyrae PLZ$_{K_s}$ relation, $K_s = -0.848 (0.007) -2.320 (0.006) \log P + 0.166 (0.011) {\rm[Fe/H]}$, anchored with {\it Gaia} EDR3 distances and theoretically predicted relations, and simultaneously estimate precise RR Lyrae based distances to these globular clusters., Comment: 18 pages, 10 figures, 4 Tables, Final Version, Accepted in The Astrophysical Journal

We present a preliminary analysis of comet P/2019 LM₄ (Palomar) as observed by the Zwicky Transient Facility (ZTF) survey in 2019 and 2020. We find that the discovery of the comet in 2019 and the recovery in 2020 is largely attributed to two separate outbursts that are ≳2 and ≳3.9 mag in strength. The two outbursts occurred between the end of April and early May in 2019, and between 2020 May 8.31 and 9.52 UTC.