arXiv subjects

Mansi M. Kasliwal

Publications and source records attributed to Mansi M. Kasliwal.

At least 163 records · Page 9Linked to original sources

arXiv2021

Multi-wavelength Observations of AT2019wey: a New Candidate Black Hole Low-mass X-ray Binary

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.

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arXiv2021

Discovery of a 310-day Period from the Enshrouded Massive System NaSt1 (WR 122)

We present optical and infrared (IR) light curves of NaSt1, also known as Wolf-Rayet (WR) 122, with observations from Palomar Gattini-IR (PGIR), the Zwicky Transient Facility (ZTF), the Katzman Automatic Imaging Telescope (KAIT), the Asteroid Terrestrial-impact Last Alert System (ATLAS), and the All-Sky Automated Survey for Supernovae (ASAS-SN). We identify a $P=309.7\pm0.7$ d photometric period from the optical and IR light curves that reveal periodic, sinusoidal variability between 2014 July and 2021 July. We also present historical IR light curves taken between 1983 July and 1989 May, which show variability consistent with the period of the present-day light curves. In the past, NaSt1 was brighter in the $J$ band with larger variability amplitudes than the present-day PGIR values, suggesting that NaSt1 exhibits variability on longer ($\gtrsim$ decade) timescales. Sinusoidal fits to the recent optical and IR light curves show that the amplitude of NaSt1's variability differs at various wavelengths and also reveal significant phase offsets of $17.0\pm2.5$ d between the ZTF $r$ and PGIR $J$ light curves. We interpret the $310$ d photometric period from NaSt1 as the orbital period of an enshrouded massive binary. We suggest that the photometric variability of NaSt1 may arise from variations in the line-of-sight optical depth toward circumstellar optical/IR emitting regions throughout its orbit due to colliding-wind dust formation. We speculate that past mass transfer in NaSt1 may have been triggered by Roche-lobe overflow (RLOF) during an eruptive phase of an Ofpe/WN9 star. Lastly, we argue that NaSt1 is no longer undergoing RLOF mass transfer.

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arXiv2021

The Blue Supergiant Progenitor of the Supernova Imposter AT~2019krl

Extensive archival \textit{Hubble Space Telescope}, \textit{Spitzer Space Telescope}, and Large Binocular Telescope imaging of the recent intermediate-luminosity transient, AT~2019krl in M74, reveal a bright optical and mid-infrared progenitor star. While the optical peak of the event was missed, a peak was detected in the infrared with an absolute magnitude of $M_{4.5\,μ{\rm m}} = -18.4$ mag, leading us to infer a visual-wavelength peak absolute magnitude of $-$13.5 to $-$14.5. The pre-discovery light curve indicated no outbursts over the previous 16\,yr. The colors, magnitudes, and inferred temperatures of the progenitor best match a 13--14 M$_{\sun}$ yellow or blue supergiant (BSG), if only foreground extinction is taken into account, or a hotter and more massive star, if any additional local extinction is included. A pre-eruption spectrum of the star reveals strong H$α$ and [N~{\sc ii}] emission with wings extending to $\pm 2000$\,km\,s$^{-1}$. The post-eruption spectrum is fairly flat and featureless with only H$α$, \ion{Na}{1}~D, [\ion{Ca}{2}], and the \ion{Ca}{2} triplet in emission. As in many previous intermediate-luminosity transients, AT~2019krl shows remarkable observational similarities to luminous blue variable (LBV) giant eruptions, SN~2008S-like events, and massive-star mergers. However, the information about the pre-eruption star favors either a relatively unobscured BSG or a more extinguished LBV with $M > 20$\,M$_{\sun}$ likely viewed pole-on.

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arXiv2021

DBSP_DRP: A Python package for automated spectroscopic data reduction of DBSP data

DBSP_DRP is a python package that provides fully automated data reduction of data taken by the Double Spectrograph (DBSP) at the 200-inch Hale Telescope at Palomar Observatory (Oke & Gunn, 1982). The underlying data reduction functionality to extract 1D spectra, perform flux calibration and correction for atmospheric absorption, and coadd spectra together is provided by PypeIt (Prochaska et al., 2020). The new functionality that DBSP_DRP brings is in orchestrating the complex data reduction process by making smart decisions so that no user input is required after verifying the correctness of the metadata in the raw FITS files in a table-like GUI. Though the primary function of DBSP_DRP is to automatically reduce an entire night of data without user input, it has the flexibility for astronomers to fine-tune the data reduction with GUIs for manually identifying the faintest objects, as well as exposing the full set of PypeIt parameters to be tweaked for users with particular science needs. DBSP_DRP also handles some of the occasional quirks specific to DBSP, such as swapping FITS header cards, adding (an) extra null byte/s to FITS files making them not conform to the FITS specification, and not writing the coordinates of the observation to file. Additionally, DBSP_DRP contains a quicklook script for making real-time decisions during an observing run, and can open a GUI displaying a minimally reduced exposure in under 15 seconds. Docker containers are available for ease of deploying DBSP_DRP in its quicklook configuration (without some large atmospheric model files) or in its full configuration.

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arXiv2021

Cataclysmic Variables in the Second Year of the Zwicky Transient Facility

Using a filter in the GROWTH Marshal based on color and the amplitude and the timescale of variability, we have identified 372 objects as known or candidate cataclysmic variables (CVs) during the second year of operation of the Zwicky Transient Facility (ZTF). From the available difference imaging data, we found that 93 are previously confirmed CVs, and 279 are strong candidates. Spectra of four of the candidates confirm them as CVs by the presence of Balmer emission lines, while one of the four has prominent HeII lines indicative of containing a magnetic white dwarf. Gaia EDR3 parallaxes are available for 154 of these systems, resulting in distances from 108-2096 pc and absolute magnitudes in the range of 7.5-15.0, with the largest number of candidates between 10.5-12.5. The total numbers are 21% higher than from the previous year of the survey with a greater number of distances available but a smaller percentage of systems close to the Galactic plane. Comparison of these findings with a machine learning method of searching all the light curves reveals large differences in each dataset related to the parameters involved in the search process.

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arXiv2021

Discovery and confirmation of the shortest gamma ray burst from a collapsar

Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T90 >2 s) have been attributed to the collapse of peculiar massive stars (collapsars). The discovery of SN 1998bw/GRB 980425 marked the first association of a LGRB with a collapsar and AT 2017gfo/GRB 170817A/GW170817 marked the first association of a SGRB with a binary neutron star merger, producing also gravitational wave (GW). Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi Satellite and the InterPlanetary Network (IPN) localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova (KN), but is consistent with being the supernova (SN). Despite the GRB duration being short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirms a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.

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arXiv2021

Design Requirements for the Wide-field Infrared TransientExplorer (WINTER)

The Wide-field Infrared Transient Explorer (WINTER) is a 1x1 degree infrared survey telescope under development at MIT and Caltech, and slated for commissioning at Palomar Observatory in 2021. WINTER is a seeing-limited infrared time-domain survey and has two main science goals: (1) the discovery of IR kilonovae and r-process materials from binary neutron star mergers and (2) the study of general IR transients, including supernovae, tidal disruption events, and transiting exoplanets around low mass stars. We plan to meet these science goals with technologies that are relatively new to astrophysical research: hybridized InGaAs sensors as an alternative to traditional, but expensive, HgCdTe arrays and an IR-optimized 1-meter COTS telescope. To mitigate risk, optimize development efforts, and ensure that WINTER meets its science objectives, we use model-based systems engineering (MBSE) techniques commonly featured in aerospace engineering projects. Even as ground-based instrumentation projects grow in complexity, they do not often have the budget for a full-time systems engineer. We present one example of systems engineering for the ground-based WINTER project, featuring software tools that allow students or staff to learn the fundamentals of MBSE and capture the results in a formalized software interface. We focus on the top-level science requirements with a detailed example of how the goal of detecting kilonovae flows down to WINTER's optical design. In particular, we discuss new methods for tolerance simulations, eliminating stray light, and maximizing image quality of a fly's-eye design that slices the telescope's focus onto 6 non-buttable, IR detectors. We also include a discussion of safety constraints for a robotic telescope.

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arXiv2021

Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically-discovered Gamma-ray Burst Afterglows and New Constraints on the Kilonova Rate

While optical surveys regularly discover slow transients like supernovae on their own, the most common way to discover extragalactic fast transients, fading away in a few nights, is via follow-up observations of gamma-ray burst and gravitational-wave triggers. However, wide-field surveys have the potential to also identify rapidly fading transients independently of such external triggers. The volumetric survey speed of the Zwicky Transient Facility (ZTF) makes it sensitive to faint and fast-fading objects as kilonovae, the optical counterparts to binary neutron stars and neutron star-black hole mergers, out to almost 200Mpc. We introduce an open-source software infrastructure, the ZTF REaltime Search and Triggering, ZTFReST, designed to identify kilonovae and fast optical transients in ZTF data. Using the ZTF alert stream combined with forced photometry, we have implemented automated candidate ranking based on their photometric evolution and fitting to kilonova models. Automated triggering of follow-up systems, such as Las Cumbres Observatory, has also been implemented. In 13 months of science validation, we found several extragalactic fast transients independent of any external trigger (though some counterparts were identified later), including at least one supernova with post-shock cooling emission, two known afterglows with an associated gamma-ray burst, two known afterglows without any known gamma-ray counterpart, and three new fast-declining sources (ZTF20abtxwfx, ZTF20acozryr, and ZTF21aagwbjr) that are likely associated with GRB200817A, GRB201103B, and GRB210204A. However, we have not found any objects which appear to be kilonovae; therefore, we constrain the rate of GW170817-like kilonovae to $R < 900$Gpc$^{-3}$yr$^{-1}$. A framework such as ZTFReST could become a prime tool for kilonova and fast transient discovery with the Vera C. Rubin Observatory.

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arXiv2021

AGN on the move: A search for off-nuclear AGN from recoiling SMBHs and ongoing galaxy mergers with the Zwicky Transient Facility

A supermassive black hole (SMBH) ejected from the potential well of its host galaxy via gravitational wave recoil carries important information about the mass ratio and spin alignment of the pre-merger SMBH binary. Such a recoiling SMBH may be detectable as an active galactic nucleus (AGN) broad line region offset by up to 10\,kpc from a disturbed host galaxy. We describe a novel methodology using forward modeling with \texttt{The Tractor} to search for such offset AGN in a sample of 5493 optically variable AGN detected with the Zwicky Transient Facility (ZTF). We present the discovery of 9 AGN which may be spatially offset from their host galaxies and are candidates for recoiling SMBHs. Five of these offset AGN exhibit double-peaked broad Balmer lines which may arise from unobscured accretion disk emission and four show radio emission indicative of a relativistic jet. The fraction of double-peaked emitters in our spatially offset AGN sample is significantly larger than the 16\% double-peaked emitter fraction observed for ZTF AGN overall. In our sample of variable AGN we also identified 52 merging galaxies, including a new spectroscopically confirmed dual AGN. Finally, we detected the dramatic rebrightening of SDSS1133, a previously discovered variable object and recoiling SMBH candidate, in ZTF. The flare was accompanied by the re-emergence of strong P-Cygni line features indicating that it may be an outbursting luminous blue variable star.

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arXiv2021

Time-series and Phasecurve Photometry of Episodically-Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200 and ZTF

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.

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arXiv2021

The Challenges Ahead for Multimessenger Analyses of Gravitational Waves and Kilonova: a Case Study on GW190425

In recent years, there have been significant advances in multi-messenger astronomy due to the discovery of the first, and so far only confirmed, gravitational wave event with a simultaneous electromagnetic (EM) counterpart, as well as improvements in numerical simulations, gravitational wave (GW) detectors, and transient astronomy. This has led to the exciting possibility of performing joint analyses of the GW and EM data, providing additional constraints on fundamental properties of the binary progenitor and merger remnant. Here, we present a new Bayesian framework that allows inference of these properties, while taking into account the systematic modeling uncertainties that arise when mapping from GW binary progenitor properties to photometric light curves. We extend the relative binning method presented in Zackay et al. (2018) to include extrinsic GW parameters for fast analysis of the GW signal. The focus of our EM framework is on light curves arising from r-process nucleosynthesis in the ejected material during and after merger, the so called kilonova, and particularly on black hole - neutron star systems. As a case study, we examine the recent detection of GW190425, where the primary object is consistent with being either a black hole (BH) or a neutron star (NS). We show quantitatively how improved mapping between binary progenitor and outflow properties, and/or an increase in EM data quantity and quality are required in order to break degeneracies in the fundamental source parameters.

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arXiv2021

Outbursting Young Stellar Object PGIR 20dci in the Perseus Arm

We report the discovery of a likely outbursting Class I young stellar object, associated with the star-forming region NGC 281-W (distance $\sim 2.8$ kpc). The source is currently seen only at infrared wavelengths, appearing in both the Palomar Gattini InfraRed ($1.2~μ$m) and the Near Earth Object Widefield Infrared Survey Explorer ($3.4$ and $4.6~μ$m) photometric time-domain surveys. Recent near-infrared imaging reveals a new, extended scattered light nebula. Recent near-infrared spectroscopy confirms the similarity of PGIR 20dci to FU Ori type sources, based on strong molecular absorption in CO, H$_2$O, and OH, weak absorption in several atomic lines, and a warm wind/outflow as indicated by a P Cygni profile in the HeI 10830 A line. This is a rare case of an FU Ori star with a well-measured long term photometric rise before a sharper outburst, and the second instance of an FU Ori star with a documented two-step brightening in the mid-infrared.

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arXiv2021

The wide-field infrared transient explorer (WINTER)

The Wide-Field Infrared Transient Explorer (WINTER) is a new infrared time-domain survey instrument which will be deployed on a dedicated 1 meter robotic telescope at Palomar Observatory. WINTER will perform a seeing-limited time domain survey of the infrared (IR) sky, with a particular emphasis on identifying r-process material in binary neutron star (BNS) merger remnants detected by LIGO. We describe the scientific goals and survey design of the WINTER instrument. With a dedicated trigger and the ability to map the full LIGO O4 positional error contour in the IR to a distance of 190 Mpc within four hours, WINTER will be a powerful kilonova discovery engine and tool for multi-messenger astrophysics investigations. In addition to follow-up observations of merging binaries, WINTER will facilitate a wide range of time-domain astronomical observations, all the while building up a deep coadded image of the static infrared sky suitable for survey science. WINTER's custom camera features six commercial large-format Indium Gallium Arsenide (InGaAs) sensors and a tiled optical system which covers a $>$1-square-degree field of view with 90% fill factor. The instrument observes in Y, J and a short-H (Hs) band tuned to the long-wave cutoff of the InGaAs sensors, covering a wavelength range from 0.9 - 1.7 microns. We present the design of the WINTER instrument and current progress towards final integration at Palomar Observatory and commissioning planned for mid-2021.

astro-ph.IM↗

arXiv2021

A population of heavily reddened, optically missed novae from Palomar Gattini-IR: Constraints on the Galactic nova rate

The nova rate in the Milky Way remains largely uncertain, despite its vital importance in constraining models of Galactic chemical evolution as well as understanding progenitor channels for Type Ia supernovae. The rate has been previously estimated in the range of $\approx10-300$ yr$^{-1}$, either based on extrapolations from a handful of very bright optical novae or the nova rates in nearby galaxies; both methods are subject to debatable assumptions. The total discovery rate of optical novae remains much smaller ($\approx5-10$ yr$^{-1}$) than these estimates, even with the advent of all-sky optical time domain surveys. Here, we present a systematic sample of 12 spectroscopically confirmed Galactic novae detected in the first 17 months of Palomar Gattini-IR (PGIR), a wide-field near-infrared time domain survey. Operating in $J$-band ($\approx1.2$ $μ$m) that is relatively immune to dust extinction, the extinction distribution of the PGIR sample is highly skewed to large extinction values ($> 50$% of events obscured by $A_V\gtrsim5$ mag). Using recent estimates for the distribution of mass and dust in the Galaxy, we show that the observed extinction distribution of the PGIR sample is commensurate with that expected from dust models. The PGIR extinction distribution is inconsistent with that reported in previous optical searches (null hypothesis probability $< 0.01$%), suggesting that a large population of highly obscured novae have been systematically missed in previous optical searches. We perform the first quantitative simulation of a $3π$ time domain survey to estimate the Galactic nova rate using PGIR, and derive a rate of $\approx 46.0^{+12.5}_{-12.4}$ yr$^{-1}$. Our results suggest that all-sky near-infrared time-domain surveys are well poised to uncover the Galactic nova population.

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arXiv2021

The peculiar Ca-rich SN 2019ehk: Evidence for a Type IIb core-collapse supernova from a low mass stripped progenitor

The nature of the peculiar `Ca-rich' SN 2019ehk in the nearby galaxy M100 remains unclear. Its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium detonation event. Here, we present very late-time photometry of the transient obtained with the Keck I telescope at $\approx280$ days from peak light. Using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an [O I] luminosity of $(0.19-1.08)\times10^{38}$ erg s$^{-1}$ and [Ca II] luminosity of $(2.7-15.6)\times10^{38}$ erg s$^{-1}$ over the range of the uncertain extinction along the line of sight. We use these measurements to derive lower limits on the synthesized oxygen mass of $\approx0.004-0.069$ M$_\odot$. The oxygen mass is a sensitive tracer of the progenitor mass for core-collapse supernovae, and our estimate is consistent with explosions of very low mass CO cores of $1.45-1.5$ M$_\odot$, corresponding to He core masses of $\approx1.8-2.0$ M$_\odot$. We present high quality peak light optical spectra of the transient and highlight features of hydrogen in both the early (`flash') and photospheric phase spectra, that suggest the presence of $\gtrsim0.02$ M$_\odot$ of hydrogen in the progenitor at the time of explosion. The presence of H, together with the large [Ca II]/[O I] ratio ($\approx10-15$) in the nebular phase is consistent with SN 2019ehk being a Type IIb core-collapse supernova from a stripped low mass ($\approx9-9.5$ M$_\odot$) progenitor, similar to the Ca-rich SN IIb iPTF 15eqv. These results provide evidence for a likely class of `Ca-rich' core-collapse supernovae from stripped low mass progenitors in star forming environments, distinct from the thermonuclear Ca-rich gap transients in old environments.

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arXiv2021

Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS), using Hubble, Spitzer, ZTF, Keck, APO and GROWTH Visible & Infrared Imaging and Spectroscopy

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD$_2$ taken with HST/WFC3, Spitzer/IRAC, the GROWTH telescope network, visible spectroscopy from Keck/LRIS and archival ZTF observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD$_2$ has a radius between 0.2-1.8 km assuming a 0.08 albedo and a coma dominated by $\sim$100$μ$ m-scale dust ejected at $\sim$1 m/s speeds with a $\sim$1'' jet pointing in the SW direction. LD$_2$ experienced a total dust mass loss of $\sim$10$^8$ kg at a loss rate of $\sim$6 kg/s with Af$ρ$/cross-section varying between $\sim$85 cm/125 km$^2$ and $\sim$200 cm/310 km$^2$ from 2019 April 9 to 2019 Nov 8. If the increase in Af$ρ$/cross-section remained constant, it implies LD$_2$'s activity began $\sim$2018 November when within 4.8 au of the Sun, implying the onset of H$_2$O sublimation. We measure CO/CO$_2$ gas production of $\lesssim$10$^{27}$ mol/s /$\lesssim$10$^{26}$ mol/s from our 4.5 $μ$m Spitzer observations, $g$-$r$ = 0.59$\pm$0.03, $r$-$i$ = 0.18$\pm$0.05, $i$-$z$ = 0.01$\pm$0.07 from GROWTH observations, H$_2$O gas production of $\lesssim$80 kg/s scaling from our estimated $C_2$ production of $Q_{C_2}\lesssim$7.5$\times10^{24}$ mol/s from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD$_2$ is similar to Jupiter family comets having close encounters with Jupiter within $\sim$0.5 Hill radius in the last $\sim$3 y, within 0.8 Hill radius in $\sim$9 y. Additionally, 78.8$\%$ of our orbital clones are ejected from the Solar System within $1 \times 10^{6}$ years having a dynamical half-life of 3.4 $\times 10^5$ years.

astro-ph.EP↗

arXiv2021

Revealing Efficient Dust-Formation at Low Metallicity in Extragalactic Carbon-Rich Wolf-Rayet Binaries

We present Spitzer/IRAC observations of dust formation from six extragalactic carbon-rich Wolf-Rayet (WC) binary candidates in low-metallicity (Z $\lesssim0.65$ Z$_\odot$) environments using multi-epoch mid-infrared (IR) imaging data from the SPitzer InfraRed Intensive Transients Survey (SPIRITS). Optical follow-up spectroscopy of SPIRITS~16ln, 19q, 16df, 18hb, and 14apu reveals emission features from C IV $\lambda5801\text{-}12$~and/or the C III-IV $\lambda4650$ He II $\lambda4686$~blend that are consistent with early-type WC stars. We identify SPIRITS~16ln as the variable mid-IR counterpart of the recently discovered colliding-wind WC4+O binary candidate, N604-WRXc, located in the sub-solar metallicity NGC 604 H II~region in M33. We interpret the mid-IR variability from SPIRITS~16ln as a dust-formation episode in an eccentric colliding-wind WC binary. SPIRITS~19q, 16df, 14apu, and 18hb exhibit absolute [3.6] magnitudes exceeding one of most IR-luminous dust-forming WC systems known, WR~104 (M$_\mathrm{[3.6]}\lesssim-12.3$). An analysis of dust formation in the mid-IR outburst from SPIRITS~19q reveals a high dust production rate of $\dot{M}_d\gtrsim2\times10^{-6}$ M$_\odot$ yr$^{-1}$, which may therefore exceed that of the most efficient dust-forming WC systems known. We demonstrate that efficient dust-formation is feasible from early-type WC binaries in the theoretical framework of colliding-wind binary dust formation if the systems host an O-type companion with a high mass-loss rate ($\dot{M}\gtrsim1.6\times10^{-6}$ M$_\odot$ yr$^{-1}$). This efficient dust-formation from early-type WC binaries highlights their potential role as significant sources of dust in low-metallicity environments.

astro-ph.GA↗

arXiv2020

Census of R Coronae Borealis stars I: Infrared light curves from Palomar Gattini IR

We are undertaking the first systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, beginning with IR light curves from the Palomar Gattini IR (PGIR) survey. PGIR is a 30 cm $J$-band telescope with a 25 deg$^{2}$ camera that is surveying 18000 deg$^{2}$ of the northern sky ($δ>-28^{o}$) at a cadence of 2 days. We present PGIR light curves for 922 RCB candidates selected from a mid-IR color-based catalog (Tisserand et al. 2020). Of these 922, 149 are promising RCB candidates as they show pulsations or declines similar to RCB stars. Majority of the candidates that are not RCB stars are either long period variables (LPVs) or RV-Tauri stars. We identify IR color-based criteria to better distinguish between RCB stars and LPVs. As part of a pilot spectroscopic run, we obtained NIR spectra for 26 out of the 149 promising candidates and spectroscopically confirm 11 new RCB stars. We detect strong He I $λ10830$ features in spectra of all RCB stars, likely originating within high velocity (200-400 km-s$^{-1}$) winds in their atmospheres. 9 of these RCB stars show $^{12}$C$^{16}$O and $^{12}$C$^{18}$O molecular absorption features, suggesting that they are formed through a white dwarf merger. We detect quasi-periodic pulsations in the light curves of 5 RCB stars. The periods range between 30-125 days and likely originate from the strange-mode instability in these stars. Our pilot run results motivate a dedicated IR spectroscopic campaign to classify all RCB candidates.

astro-ph.SR↗