10 research outputs found
Initial Visible and Mid-IR Characterization of P/2019 LDâ (ATLAS), an Active Transitioning Centaur Among the Trojans, with Hubble, Spitzer, ZTF, Keck, APO and GROWTH Imaging and Spectroscopy
We present visible and mid-infrared imagery and photometry of Jovian co-orbital comet P/2019 LDâ (ATLAS) taken with Hubble Space Telescope/WFC3 on 2020 April 1, Spitzer Space Telescope/IRAC on 2020 January 25, Zwicky Transient Facility between 2019 April 9 and 2019 Nov 8 and the GROWTH telescope network from 2020 May to July, as well as visible spectroscopy from Keck/LRIS on 2020 August 19. Our observations indicate that LDâ has a nucleus with radius 0.2-1.8 km assuming a 0.08 albedo and that the coma is dominated by âŒ100 ÎŒ m-scale dust ejected at âŒ1 m/s speeds with a âŒ1" jet pointing in the SW direction. LDâ experienced a total dust mass loss of âŒ10âž kg and dust mass loss rate of âŒ6 kg/s with AfÏ/cross-section varying between âŒ85 cm/125 kmÂČ and âŒ200 cm/310 kmÂČ between 2019 April 9 and 2019 Nov 8. If the AfÏ/cross-section increase remained constant, it implies that LDâ has remained active since âŒ2018 November when it came within 4.8 au of the Sun, a typical distance for comets to begin sublimation of HâO. From our 4.5 ÎŒm Spitzer observations, we set a limit on CO/COâ gas production of âŒ10ÂČâ·/âŒ10ÂČⶠmol/s. Multiple bandpass photometry of LDâ taken by the GROWTH network measured in a 10,000 km aperture provide color measurements of g-r = 0.59±0.03, r-i = 0.18±0.05, and i-z = 0.01±0.07, colors typical of comets. We set a spectroscopic upper limit to the production of HâO gas of âŒ80 kg/s. Improving the orbital solution for LDâ with our observations, we determine that the long-term orbit of LDâ is that of a typical Jupiter Family Comet having close encounters with Jupiter coming within âŒ0.5 Hill radius in the last âŒ3 y to within 0.8 Hill radius in âŒ9 y and has a 95% chance of being ejected from the Solar System in < 10 Myr
Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3
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 degÂČ, a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10â»ÂČâ” yrâ»Âč. 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 (â16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than â16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag dayâ»Âč (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 â16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than 10â»âŽ, or Ï > 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 â16 mag would constrain the maximum fraction of bright kilonovae to <25%
Single-dot spectroscopy in high magnetic fields
NRC publication: Ye
Characterization of the Nucleus, Morphology, and Activity of Interstellar Comet 2I/Borisov by Optical and Near-infrared GROWTH, Apache Point, IRTF, ZTF, and Keck Observations
International audienceWe present visible and near-infrared (NIR) photometric and spectroscopic observations of interstellar object (ISO) 2I/Borisov taken from 2019 September 10 to 2019 December 20 using the GROWTH, the Apache Point Observatory Astrophysical Research Consortium 3.5 m, and the NASA Infrared Telescope Facility 3.0 m combined with pre- and postdiscovery observations of 2I obtained by the Zwicky Transient Facility from 2019 March 17 to 2019 May 5. Comparison with imaging of distant solar system comets shows an object very similar to mildly active solar system comets with an outgassing rate of âŒ1027 mol sâ1. The photometry, taken in filters spanning the visible and NIR range, shows a gradual brightening trend of âŒ0.03 mag dayâ1 since 2019 September 10 UTC for a reddish object becoming neutral in the NIR. The light curve from recent and prediscovery data reveals a brightness trend suggesting the recent onset of significant H2O sublimation with the comet being active with super volatiles such as CO at heliocentric distances >6 au consistent with its extended morphology. Using the advanced capability to significantly reduce the scattered light from the coma enabled by high-resolution NIR images from Keck adaptive optics taken on 2019 October 4, we estimate a diameter for 2Iâs nucleus of âČ1.4 km. We use the size estimates of 1I/âOumuamua and 2I/Borisov to roughly estimate the slope of the ISO size distribution, resulting in a slope of âŒ3.4 ± 1.2, similar to solar system comets and bodies produced from collisional equilibrium
Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3
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 <57% (<89%) of putative kilonovae could be brighter than-16.6 mag assuming flat evolution (fading by 1 mag day-1) at the 90% confidence level. If we further take into account the online terrestrial probability for each GW trigger, we find that no more than <68% of putative kilonovae could be brighter than-16.6 mag. Comparing to model grids, we find that some kilonovae must have M ej < 0.03 M oË, X lan > 10-4, or Ï > 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 <25%