Year: 2020
Type: article
Abstract: 2I/Borisov is the first-ever observed interstellar comet (and the second detected interstellar object (ISO)). It was discovered on 2019 August 30 and has a heliocentric orbital eccentricity of ∼3.35, corresponding to a hyperbolic orbit that is unbound to the Sun. Given that it is an ISO, it is of interest to compare its properties—such as composition and activity—with the comets in our solar system. This study reports low-resolution optical spectra of 2I/Borisov. The spectra were obtained by the MDM Observatory Hiltner 2.4 m telescope/Ohio State Multi-Object Spectrograph (on 2019 October 31.5 and November 4.5, UT). The wavelength coverage spanned from 3700 to 9200 Å. The dust continuum reflectance spectra of 2I/Borisov show that the spectral slope is steeper in the blue end of the spectrum (compared to the red). The spectra of 2I/Borisov clearly show CN emission at 3880 Å, as well as C2 emission at both 4750 and 5150 Å. Using a Haser model to covert the observed fluxes into estimates for the molecular production rates, we find Q(CN) = 2.4 ± 0.2 × 1024 s−1, and Q(C2) = (5.5 ± 0.4) × 1023 s−1 at the heliocentric distance of 2.145 au. Our Q(CN) estimate is consistent with contemporaneous observations, and the Q(C2) estimate is generally below the upper limits of previous studies. We derived the ratio Q(C2)/Q(CN) = 0.2 ± 0.1, which indicates that 2I/Borisov is depleted in carbon-chain species, but is not empty. This feature is not rare for the comets in our solar system, especially in the class of Jupiter-family comets.
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: Collaborative Research: Characterizing the Trans-Neptunian Solar System with the Dark Energy Survey, SEARCH AND DISCOVERY IN THE TRANS-NEPTUNIAN SOLAR SYSTEM USING THE DARK ENERGY SURVEYWITH THE RECENT SUCCESS OF THE NEW HORIZONS MISSION AND THE HYPOTHESIS OF A VERY DISTANT PLANET NINE INTEREST IN THE TRANS-NEPTUNIAN SOLAR SYSTEM IS AT AN ALL-TIME HIGH. THIS PROPOSAL DESCRIBES AN OPPORTUNITY TO LEVERAGE AN EXTRAORDINARY DATA SET TO SHED NEW LIGHT ON THIS POORLY UNDERSTOOD REGION. THE DATA COME FROM THE DARK ENERGY SURVEY (DES) WHICH HAS BEEN AWARDED 525 NIGHTS OVER 5 YEARS (2013-2018) ON THE 4-METER BLANCO TELESCOPE AT CERRO TOLOLO IN CHILE. DES CONSISTS OF TWO INTERLEAVED SURVEYS: A WIDE SURVEY THAT IS IMAGING 5000 SQ. DEG. IN FIVE COLORS TO A LIMITING R-BAND MAGNITUDE OF ~23.8 AND A SUPERNOVA SURVEY THAT OBSERVES 30 SQ. DEG. APPROXIMATELY WEEKLY FOR SIX MONTHS EACH YEAR AT A DEPTH UP TO R~24.5. THE COMBINATION OF AREA AND DEPTH THAT MAKES DES THE WORLD S FOREMOST ONGOING COSMOLOGICAL SURVEY ALSO MAKES IT IDEALLY SUITED TO DISCOVER AND STUDY HUNDREDS OF NEW TRANS-NEPTUNIAN OBJECTS (TNOS). DES S BROAD OFF-ECLIPTIC COVERAGE ALSO MAKES THIS SURVEY PARTICULARLY SENSITIVE TO THE DYNAMICALLY DISTURBED HOT TNO POPULATIONS THAT OCCUPY HIGHER-INCLINATION ORBITS. THESE OBJECTS ENCODE THE HISTORY OF THE SOLAR SYSTEM S BIRTH ENVIRONMENT AND THE FORMATION AND MIGRATION HISTORIES OF THE GIANT PLANETS. THE MOST DISTANT TNOS DISPLAY AN ALIGNMENT IN ORBITAL AND PHYSICAL SPACE THAT MAY POINT TO THE EXISTENCE OF A DISTANT SUPER-EARTH SUCH AS THE PLANET NINE (P9) RECENTLY PROPOSED BY BATYGIN&BROWN (2016). THIS HYPOTHESIS CAN BE DECISIVELY TESTED WITH OUR DATA. WE WILL DO SO BOTH THROUGH A DIRECT SEARCH FOR P9 AND THROUGH THE DISCOVERY OR EXCLUSION OF DYNAMICALLY RELATED OBJECTS PREDICTED BY THE THEORY SUCH AS A POPULATION OF HIGH INCLINATION CENTAURS AND ADDITIONAL DISTANT ALIGNED OBJECTS. OUR DIRECT SEARCH WILL COMPLEMENT THE RECENT ANALYSIS BY FIENGA ET AL. (2016) WHICH USED THE PRECISE MEASUREMENTS OF THE DISTANCE TO SATURN OBTAINED BY NASA S CASSINI SATELLITE OVER THE PAST DECADE. THEIR ANALYSIS EXCLUDES A BROAD RANGE OF POSSIBLE P9 POSITIONS NEAR PERIHELION BUT SHOWS THAT A SMALL REGION CORRESPONDING TO A P9 TRUE ANOMALY NEAR 120 DEGREES IS FAVORED OVER THE NULL HYPOTHESIS. THIS FAVORED REGION LIES IN THE MIDDLE OF THE DES SURVEY FOOTPRINT. THE PI LEADS THE TRANSIENTS AND MOVING OBJECTS SCIENCE WORKING GROUP WITHIN DES AND HAS DISCOVERED ALL ~50 OF THE TRANS-NEPTUNIAN OBJECTS FOUND BY DES TO DATE. AMONG THESE OBJECTS IS ONE OF THE SIX OBJECTS MOST DISTANT TNOS WHOSE ALIGNED ORBITS MOTIVATED THE P9 HYPOTHESIS. THIS SEARCH BEGAN IN THE DES SUPERNOVA SURVEY FIELDS WHOSE REGULAR TEMPORAL CADENCE SIMPLIFIES THE PROBLEM OF CONNECTING OBSERVATIONS OF FROM DIFFERENT EPOCHS. WE HAVE BEGUN TO EXTEND THE SEARCH TO THE WIDE SURVEY WHOSE SPARSER TEMPORAL CADENCE LEADS TO A MORE CHALLENGING COMBINATORIC PROBLEM. A PROTOTYPE SEARCH USING ONLY 100 SQ. DEG. OF DATA (2% OF THE FULL SURVEY AREA) FROM THE 2013-14 SEASON RESULTED IN OVER A DOZEN NEW TNOS AND GIVES US CONFIDENCE THAT THE STRATEGY WE INTEND TO DEPLOY AT SCALE FOR THE FULL 5000 SQ. DEG. FIVE-YEAR WIDE SURVEY WILL BE SUCCESSFUL. THIS PROPOSAL WILL RESULT IN MULTIPLE-OPPOSITION ORBITS FOR SEVERAL HUNDRED NEW PRIMARILY HIGH-INCLINATION TNOS COMPLETE WITH MULTICOLOR PHOTOMETRY AND A WELL-CHARACTERIZED SELECTION FUNCTION. THESE DATA WILL PROVIDE US WITH AN OPPORTUNITY TO REASSESS THE DYNAMICAL HISTORY OF THE SOLAR SYSTEM. THIS PROJECT WILL INCLUDE A THEORETICAL ANALYSIS TO PROVIDE A DYNAMICAL INTERPRETATION OF THE DATA WITH A FOCUS ON EVOLUTIONARY SCENARIOS THAT PRODUCE THE OBSERVED POPULATIONS OF TNOS. WE ALSO OUTLINE A PROGRAM TO ALLOW CITIZEN SCIENTISTS TO SEARCH FOR TNOS IN PUBLIC DES DATA. THIS PROPOSAL REQUIRES NO MODIFICATIONS TO DES S TIME ALLOCATION SURVEY STRATEGY OR DATA REDUCTION PIPELINES BUT WILL GREATLY AMPLIFY THE SCIENTIFIC RETURN ON THIS DATA SET.
OpenAlex ID: W3000739601