The N$_2$ and CO-rich and water-depleted comet C/2016 R2 (Pan-STARRS) (hereafter `C/2016 R2') is a unique comet for detailed spectroscopic analysis. We aim to explore the associated photochemistry of parent species, which produces different metastable states and forbidden emissions, in this cometary coma of peculiar composition. We re-analyzed the high-resolution spectra of comet C/2016 R2, which were obtained in February 2018, using the UVES spectrograph of the European Southern Observatory (ESO) Very Large Telescope (VLT). Various forbidden atomic emission lines of [CI], [NI], and [OI] were observed in the optical spectrum of this comet when it was at 2.8 au from the Sun. The observed forbidden emission intensity ratios are studied in the framework of a couple-chemistry emission model. The model calculations show that CO$_2$ is the major source of both atomic oxygen green and red-doublet emissions in the coma of C/2016 R2 (while for most comets it is generally H$_2$O), whereas, CO and N$_2$ govern the atomic carbon and nitrogen emissions, respectively. Our modelled oxygen green to red-doublet and carbon to nitrogen emission ratios are higher by a factor {of 3}, when compared to the observations. These discrepancies can be due to uncertainties associated with photon cross sections or unknown production/loss sources. Our modelled oxygen green to red-doublet emission ratio is close to the observations, when we consider an O$_2$ abundance with a production rate of 30\% relative to the CO production rate. The collisional quenching is not a significant loss process for N($^2$D) though its radiative lifetime is significant ($\sim$10 hrs). Hence, the observed [NI] doublet-emission ratio ([NI] 5198/5200) of 1.22, which is smaller than the terrestrial measurement by a factor {1.4}, is mainly due to the characteristic radiative decay of N($^2$D).
We report on imaging and spectroscopic observations of comet C/2016~R2 (Pan-STARRS) obtained with the 0.8\,m and 2.7\,m telescopes of McDonald Observatory in November and December 2017 respectively. The comet was at a heliocentric distance greater than 3\,{\sc au} during both sets of observations. The images showed a well-developed tail with properties that suggested it was an ion tail. The spectra confirmed that we were observing well-developed bands of CO$^+$ and N$_2^+$. The N$_2^+$ detection was unequivocally cometary and was one of the strongest bands of N$_2^+$ detected in a comet spectr…
We carried out observations of a peculiar comet, C/2016 R2 (Pan-STARRS), using a low resolution spectrograph mounted on the 1.2m telescope at Mount Abu Infrared Observatory, India. The comet was observed on two dates in January 2018, when it was at a heliocentric distance of 2.8 AU. Study based on our observations revealed that the optical spectrum of this comet is quite unusual as compared to general cometary spectra. Most of the major cometary emissions like C$_{2}$, C$_{3}$ and CN were absent in comet C/2016 R2. However, the comet spectrum showed very strong emission bands from ionic specie…
Main Belt Comets are a recently identified population of minor bodies with stable asteroid-like orbits but cometary appearances. Sublimation of water ice is the most likely mechanism for their recurrent activity (i.e. dust tails and dust comae), although there has been no direct detection of gas. These peculiar objects could hold the key to the origin of water on Earth. In this paper we present a search for the gas responsible for lifting dust from P/2012 T1 (Pan-STARRS), and review previous attempts at such measurements. To date such searches have mainly been indirect, looking for the common …
Dynamically new comet C/2011 L4 (PanSTARRS) is one of the brightest comets since the great comet C/1995 O1 (Hale-Bopp). Here, we present our multi-wavelength observations of C/2011 L4 during its in-bound passage to the inner Solar system. A strong absorption band of water ice at 2.0 $μ$m was detected in the near infrared spectra, taken with the 8-m Gemini-North and 3-m IRTF telescopes. The companion 1.5 $μ$m band of water ice, however, was not observed. Spectral modeling show that the absence of the 1.5 $μ$m feature can be explained by the presence of sub-micron-sized fine ice grains. No gas l…
We present pre-perihelion infrared 8 to 31 micron spectrophotometric and imaging observations of comet C/2012 K1 (Pan-STARRS), a dynamically new Oort Cloud comet, conducted with NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) facility (+FORCAST) in 2014 June. As a "new" comet (first inner solar system passage), the coma grain population may be extremely pristine, unencumbered by a rime and insufficiently irradiated by the Sun to carbonize its surface organics. The comet exhibited a weak 10 micron silicate feature ~1.18 +/- 0.03 above the underlying best-fit 215.32 +/- 0.95 K co…
The recent observations show that comet C/2016 R2 (Pan-Starrs) has a unique and peculiar composition when compared with several other comets observed at 2.8 au heliocentric distance. Assuming solar resonance fluorescence is the only excitation source, the observed ionic emission intensity ratios are used to constrain the corresponding neutral abundances in this comet. We developed a physico-chemical model to study the ion density distribution in the inner coma of this comet by accounting for photon and electron impact ionization of neutrals, charge exchange and proton transfer reactions betwee…
We introduce a new technique to estimate the comet nuclear size frequency distribution (SFD) that combines a cometary activity model with a survey simulation and apply it to 150 long period comets (LPC) detected by the Pan-STARRS1 near-Earth object survey. The debiased LPC size-frequency distribution is in agreement with previous estimates for large comets with nuclear diameter $>\sim 1$~km but we measure a significant drop in the SFD slope for small objects with diameters $<1$~km and approaching only $100$~m diameter. Large objects have a slope $α_{big} = 0.72 \pm 0.09 (stat.) \pm 0.15 (sys.)…
We analyze 760475 observations of 333026 main-belt objects obtained by the Pan-STARRS1 (PS1) survey telescope between 2012 May 20 and 2013 November 9, a period during which PS1 discovered two main-belt comets, P/2012 T1 (PANSTARRS) and P/2013 R3 (Catalina-PANSTARRS). PS1 comet detection procedures currently consist of the comparison of the point spread functions (PSFs) of moving objects to those of reference stars, and the flagging of objects that show anomalously large radial PSF widths. Based on the number of missed discovery opportunities among comets discovered by other observers, we estim…
A sequence of events, dominated by two outbursts and ending with the preperihelion disintegration of comet C/2017 S3, is examined. The onset times of the outbursts are determined with high accuracy from the light curve of the nuclear condensation before it disappeared following the second outburst. While the brightness of the condensation was declining precipitously, the total brightness continued to grow in the STEREO-A's HI1 images until two days before perihelion. The red magnitudes measured in these images refer to a uniform cloud of nuclear fragments, 2200 km^2 in projected area, that beg…
Main belt asteroid (300163) 2006 VW139 (later designated P/2006 VW139) was discovered to exhibit comet-like activity by the Pan-STARRS1 survey telescope using automated point-spread-function analyses performed by PS1's Moving Object Processing System. Deep follow-up observations show both a short (\sim 10") antisolar dust tail and a longer (\sim 60") dust trail aligned with the object's orbit plane, similar to the morphology observed for another main-belt comet, P/2010 R2 (La Sagra), and other well-established comets, implying the action of a long-lived, sublimation-driven emission event. Phot…
In early April 2017, five weeks before passing through perihelion, the dust-poor comet C/2015 ER61 was observed to undergo a major outburst, during which its intrinsic brightness increased briefly by about 2 mag. Evidence is presented in this paper to suggest that the flare-up was in all likelihood a product of an event of nuclear fragmentation that gave birth to a companion nucleus, which was first detected more than nine weeks later, on June 11, and remained under observation for 19 days. The companion is found to have separated from the parent nucleus with a velocity of less than 1 m/s; sub…
We present a method to identify distant solar system objects in long-term wide-field asteroid survey data, and conduct a search for them in the Pan-STARRS1 (PS1) image data acquired from 2010 to mid-2015. We demonstrate that our method is able to find multi-opposition orbital links, and we present the resulting orbital distributions which consist of 154 Centaurs, 255 classical Trans-Neptunian Objects (TNOs), 121 resonant TNOs, 89 Scattered Disc Objects (SDOs) and 10 comets. Our results show more than half of these are new discoveries, including a newly discovered 19th magnitude TNO. Our identi…
We present the results of a Monte Carlo technique to calculate the absolute magnitudes (H) and slope parameters (G) of about 240000 asteroids observed by the Pan-STARRS1 telescope during the first 15 months of its 3-year all-sky survey mission. The system's exquisite photometry with photometric errors < 0.04 mag, and well-defined filter and photometric system, allowed us to derive accurate H and G even with a limited number of observations and restricted range in phase angles. Our Monte Carlo method simulates each asteroid's rotation period, amplitude and color to derive the most-likely H and …
We present an analysis of the photometric data of comet C/2011 L4 (PANSTARRS) observed at heliocentric distance of 4.4 - 4.2 AU. The comet C/2011 L4 (PANSTARRS) shows one significant activity, despite of its quite large heliocentric distance. The color indexes, dust mass-loss rates and radius of the comet are measured.
We present a pre-survey study of using Pan-STARRS high sampling rate video mode guide star images to search for TNOs. With suitable selection of the guide stars within the Pan-STARRS 7 deg^{2} field of view, the lightcurves of these guide stars can also be used to search for occultations by TNOs. The best target stars for this purpose are stars with high signal-to-noise ratio (SNR) and small angular size.In order to do this, we compiled a catalog using the SNR calculated from stars with m_V <13 mag in the Tycho2 catalog then cross matched these stars with the 2MASS catalog and estimated their …
In this work we report the detection of seven Neptune Trojans (NTs) in the Pan-STARRS 1 (PS1) survey. Five of these are new discoveries, consisting of four L4 Trojans and one L5 Trojan. Our orbital simulations show that the L5 Trojan stably librates for only several million years. This suggests that the L5 Trojan must be of recent capture origin. On the other hand, all four new L4 Trojans stably occupy the 1:1 resonance with Neptune for more than 1 Gyr. They can, therefore, be of primordial origin. Our survey simulation results show that the inclination width of the Neptune Trojan population s…
The rotational state of asteroids is controlled by various physical mechanisms including collisions, internal damping and the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. We have analysed the changes in magnitude between consecutive detections of approximately 60,000 asteroids measured by the PanSTARRS 1 survey during its first 18 months of operations. We have attempted to explain the derived brightness changes physically and through the application of a simple model. We have found a tendency toward smaller magnitude variations with decreasing diameter for objects of 1 < D < 8 km. Assu…
The dust emission from active asteroids is likely driven by collisions, fast rotation, sublimation of embedded ice, and combinations of these. Characterising these processes leads to a better understanding of their respective influence on the evolution of the asteroid population. We study the role of fast rotation in the active asteroid 358P (P 2012/T1). We obtained two nights of deep imaging of 358P with SOAR/Goodman and VLT/FORS2. We derived the rotational light curve from time-resolved photometry and searched for large fragments and debris > 8 mm in a stacked, ultra-deep image. The nucleus …
P/2011 S1 (Gibbs) is an outer solar system comet or active Centaur with a similar orbit to that of the famous 29P/Schwassmann-Wachmann 1. P/2011 S1 (Gibbs) has been observed by the Pan-STARRS 1 (PS1) sky survey from 2010 to 2012. The resulting data allow us to perform multi-color studies of the nucleus and coma of the comet. Analysis of PS1 images reveals that P/2011 S1 (Gibbs) has a small nucleus $< 4$ km radius, with colors $g_{P1}-r_{P1} = 0.5 \pm 0.02$, $r_{P1}-i_{P1} = 0.12 \pm 0.02$ and $i_{P1}-z_{P1} = 0.46 \pm 0.03$. The comet remained active from 2010 to 2012, with a model-dependent m…
We present a multi-wavelength study of comet C/2016 R2 (PanSTARRS). This comet was observed on 23-24 January 2018 with the IRAM 30m telescope, and in January to March 2018 with the Nançay radio telescope. Visible spectroscopy was performed in December 2017 and February 2018 with small amateur telescopes. We report on measurements of CO, CH3OH, H2CO and HCN production rates, and on the determination of the N2/CO abundance ratio. Several other species, especially OH, were searched for but not detected. The inferred relative abundances, including upper limits for sulfur species, are compared to t…
We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient detections from next-generation astronomical survey telescopes. MOPS achieves > 99.5% efficiency in producing orbits from a synthetic but realistic population of asteroids whose measurements were simulated for a Pan-STARRS4-class telescope. Additionally, using a non-physical grid population, we demonstrate that MOPS can detect populations of currently unknown objects such as interstellar asteroids. MOPS has been…
Using the first 18 months of the Pan-STARRS 1 survey we have identified 33 candidate high-amplitude objects for follow-up observations and carried out observations of 22 asteroids. 4 of the observed objects were found to have observed amplitude $A_{obs}\geq 1.0$ mag. We find that these high amplitude objects are most simply explained by single rubble pile objects with some density-dependent internal strength, allowing them to resist mass shedding even at their highly elongated shapes. 3 further objects although below the cut-off for 'high-amplitude' had a combination of elongation and rotation…
A class of asteroids, called large super-fast rotators (large SFRs), have rotation periods shorter than 2 hours and diameters larger than ~ 0.3 km. They pose challenges to the usual interior rubble-pile structure unless a relatively high bulk density is assumed. So far, only six large SFRs have been found. Therefore, we present a survey of asteroid rotation period using Pan-STARRS 1 telescopes during 2016 October 26 to 31 to search more large SFRs and study their properties. A total of 876 reliable rotation periods are measured, among which seven are large SFRs, thereby increasing the inventor…
We present analysis of observations of CO2 and OI emission in three comets to measure the CO2 abundance and evaluate the possibility of employing observations of OI emission in comets as a proxy for CO2. We obtained NIR imaging sensitive to CO2 of comets C/2012 K1 (PanSTARRS), C/2012 K5 (LINEAR), and 290P/Jager with the IRAC instrument on Spitzer. We acquired observations of OI emission in these comets with the ARCES echelle spectrometer mounted on the 3.5-meter telescope at Apache Point Observatory and observations of OH with the Swift observatory (PanSTARRS) and with Keck HIRES (Jager). The …
Centaurs are small bodies orbiting in the giant planet region which were scattered inwards from their source populations beyond Neptune. Some members of the population display comet-like activity during their transition through the solar system, the source of which is not well understood. The range of heliocentric distances where the active Centaurs have been observed, and their median lifetime in the region suggest this activity is neither driven by water-ice sublimation, nor entirely by super-volatiles. Here we present an observational and thermo-dynamical study of 13 Centaurs discovered in …
We present new parallax measurements from the CFHT Infrared Parallax Program and the Pan-STARRS 3$π$ Steradian Survey for the young ($\approx150-300$ Myr) triple system VHS J125601.92$-$125723.9. This system is composed of a nearly equal-flux binary ("AB") and a wide, possibly planetary-mass companion ("b"). The system's published parallactic distance ($12.7\pm1.0$ pc) implies absolute magnitudes unusually faint compared to known young objects and is in tension with the spectrophotometric distance for the central binary ($17.2\pm2.6$ pc). Our CFHT and Pan-STARRS parallaxes are consistent, and …
On 21 March 2013 high-resolution slit spectrographs of comet C/2011 L4 (Panstarrs), at the heliocentric distance r = 0.46 Astronomical Units (AU), were obtained at the Osservatorio Astronomico Campo dei Fiori, Italy. Emission lines of sodium were the strongest in the spectrum as is common in comets, but also potassium lines were detected. These have been rarely observed in comets since the apparition of brightest comet C/1965 S1 (Ikeya-Seki). Lithium was not detected, and stringent upper limits of its abundance compared to other alkali were derived. We obtain abundance ratios Na/K = 54 +/-14 a…
Observations of comet C/2016 R2 (PanSTARRS) have revealed exceptionally bright emission bands of N$_2^+$, the strongest ever observed in a comet spectrum. Alternatively, it appears to be poor in CN compared to other comets, and remarkably depleted in H$_2$O. Here we quantify the N$_2$ production rate from N$_2^+$ emission lines using the Haser model. We derived effective parent and daughter scalelengths for N2 producing N2+. This is the first direct measurement of such parameters. Using a revised fluorescence efficiency for N2+, the resulting production rate of molecular nitrogen is inferred t…
Optical observations of the Oort cloud comet C/2017 K2 (PANSTARRS) show that its activity began at large heliocentric distances (up to 35 au), which cannot be explained by either the sublimation or the crystallization of water ice. Supervolatile sublimation, most likely of carbon monoxide (CO), has been proposed as a plausible driver of the observed mass loss. Here, we present the detection of the J = 2$-$1 rotational transition in outgassed CO from C/2017 K2 when at heliocentric distance $r_H$ = 6.72 au, using the James Clerk Maxwell Telescope. The CO line is blue-shifted by 0.20$\pm$0.03 km …
Comet C/2016 R2 (PanSTARRS) has a peculiar volatile composition, with CO being the dominant volatile as opposed to H$_2$O and one of the largest N$_2$/CO ratios ever observed in a comet. Using observations obtained with the \textit{Spitzer Space Telescope}, NASA's Infrared Telescope Facility, the 3.5-meter ARC telescope at Apache Point Observatory, the Discovery Channel Telescope at Lowell Observatory, and the Arizona Radio Observatory 10-m Submillimeter Telescope we quantified the abundances of 12 different species in the coma of R2 PanSTARRS. We confirm the high abundances of CO and N$_2$ an…
We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations of the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst. These measurements of HCN, CS, CH$_3$OH, H$_2$CO, and HNC (along with continuum emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrela…
Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. We obtained high resolution spectra of the comet in February when it was at 2.8 au from the Sun. We used the UVES spectrograph of the ESO VLT, complemented with narrow-band images obtained with the TRAPPIST telescopes. We detect strong emissions from the ions $\mathrm{N_2^+}$ and $\mathrm{CO^+}$, but also $\mathrm{CO_2^+}$, emission from the CH radical, and much fainter emissions of the CN, $\mathrm{C_2}$, and $\mathrm{C_3}$ radicals which were not detected in previous observations…
We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of 1.012 au and 0.026 au, respectively, approximately 30 hours before its closest approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution ($λ$/$Δλ$~250) spectroscopic observations in the N-band and imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7 and 18.8 $μ$m) in the N- and Q-bands were obtained using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru telescope atop …
Microlensing events can be used to directly measure the masses of single field stars to a precision of $\sim$1-10\%. The majority of direct mass measurements for stellar and sub-stellar objects typically only come from observations of binary systems. Hence microlensing provides an important channel for direct mass measurements of single stars. The Gaia satellite has observed $\sim$1.7 billion objects, and analysis of the second data release has recently yielded numerous event predictions for the next few decades. However, the Gaia catalog is incomplete for nearby very-low-mass objects such as …
Orbital elements of C2011 L4 (PanStarrs) Oort cloud comet, computed by MPC (Minor Planet Center, Minor Planet Electronic Circular 2012-T08), show that the closest approach to the Sun occurred on 2013 March 10th, at about 0.3 A.U., then about 4,51x10^7 km. Discovered by Richard Wainscoat (Institute for Astronomy, University of Hawaii) on four CCD images taken with the 1.8-m "Pan-STARRS 1" telescope at Haleakala taken on 2011 June 6th. My first observation of the comet was on 2013 March 10th whit the comet visible in the twilight. I did the following visual estimation; Mar. 10.73,-1.0*,5'(T. Sca…
Recent observations of the long period comet C/2016 R2 (PanSTARRS) indicate an unusually high N2/CO abundance ratio, typically larger than 0.05, and at least 2-3 times higher than the one measured in 67P/Churyumov-Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O, compared to other comets. Here, we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed…
We have combined optical and NIR photometry from Pan-STARRS 1 and UKIDSS to search the young (5-10 Myr) star-forming region of Upper Scorpius for wide (~400-4000 AU) substellar companions down to ~5 Mjup. Our search is ~4mag deeper than previous work based on 2MASS. We identified several candidates around known stellar members using a combination of color selection and spectral energy distribution fitting. Our followup spectroscopy has identified two new companions as well as confirmed two companions previously identified from photometry, with spectral types of M7.5-M9 and masses of ~15-60 Mju…
We present a spectro-photometric analysis of 2880 cool white dwarfs within 100 pc of the Sun and cooler than Teff = 10,000 K, with grizy Pan-STARRS photometry and Gaia trigonometric parallaxes available. We also supplement our data sets with near-infrared JHK photometry, when available, which is shown to be essential for interpreting the coolest white dwarfs in our sample. We perform a detailed analysis of each individual object using state-of-the-art model atmospheres appropriate for each spectral type including DA, DC, DQ, DZ, He-rich DA, and the so-called IR-faint white dwarfs. We discuss t…
We present our results on the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer (ACIS) observations of the bright Oort Cloud comets C/2012 S1 (ISON) and C/2011 L4 (PanSTARRS). ISON was observed between 2013 October 31-November 06 during variable speed solar wind (SW), and PanSTARRS was observed between 2013 April 17-23 during fast SW. ISON produced an extended parabolic X-ray morphology consistent with a collisionally thick coma, while PanSTARRS demonstrated only a diffuse X-ray-emitting region. We consider these emissions to be from charge exchange (CX) and model each comet's emissi…
