Backyard Worlds: Planet 9 Discovery of an Unusual Low-mass Companion to an M Dwarf at 80 pc
Austin Rothermich, Adam C. Schneider, Jacqueline K. Faherty, Katelyn Allers, Daniella Bardalez-Gagliuffi, Aaron M. Meisner, Marc Kuchner, J. Davy Kirkpatrick, Dan Caselden, Paul Beaulieu
DDraft version February 8, 2021
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Backyard Worlds: Planet 9 discovery of an unusual low-mass companion to an M Dwarf at 80 pc
Austin Rothermich, Adam C. Schneider,
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Jacqueline K. Faherty, Katelyn Allers, Daniella Bardalez-Gagliuffi, Aaron M. Meisner, Marc Kuchner, J. Davy Kirkpatrick, Dan Caselden, and Paul Beaulieu Physics Department, University Of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816, USA US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002, USA Department of Physics and Astronomy, George Mason University, MS3F3, 4400 University Drive, Fairfax, VA 22030, USA Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, NY 10024, USA Bucknell University; Department of Physics and Astronomy; Lewisburg, PA 17837, USA NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771, USA IPAC, Mail Code 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA Gigamon Applied Threat Research, 619 Western Avenue, Suite 200, Seattle, WA 98104, USA Backyard Worlds: Planet 9
ABSTRACTWe present the discovery of CWISE J203546.35-493611.0, a peculiar M8 companion to the M4.5 starAPMPM J2036-4936 discovered through the citizen science project Backyard Worlds: Planet 9. GivenCWISE J203546.35-493611.0’s proper motion ( µ α , µ δ ) = ( − ± − ±
23) and angular separationof 34.2 (cid:48)(cid:48) from APMPM 2036-4936, we calculate a chance alignment probability of 1 . × − . Bothstars in this system appear to be underluminous, and the spectrum obtained for CWISE J203546.35-493611.0 shows a triangular H band. Further study of this system is warranted to understand thesepeculiarities. INTRODUCTIONLow-mass companions to known stars provide an excellent opportunity to better understand the formation andevolution of these objects. Identifying co-moving companions has been made easier through the use of all sky, multi-epoch surveys such as the Wide-field Infrared Survey Explorer ( WISE ; Wright et al. 2010). Backyard Worlds: Planet9 (Kuchner et al. 2017) is a citizen science project where volunteers examine
WISE images to identify high propermotion objects. Here we report the discovery of CWISE J203546.35-493611.0 (hereafter CWISE J2035-4936) an objectat the M/L spectral type boundary co-moving with a known M4.5 star found through the Backyard Worlds project.DISCOVERY OF COMPANIONThe primary of this system, APMPM J2036-4936, was discovered and classified via an optical spectrum as M4.5in Lodieu et al. (2005). Those authors estimated a distance of 165.8 pc to APMPM J2036-4936 using photometric-spectral type relations, resulting in a tangential velocity estimate of 335 km s − . Using the parallax measurementfor this object from Gaia DR2 (Gaia Collaboration et al. 2018), we find a new distance of 81.5 ± − . Using this new distance along with the Gaia DR2 G magnitude for APMPMJ2036-4936 of G=18.080 ± ± ± ± ± ± a r X i v : . [ a s t r o - ph . S R ] F e b Figure 1.
Left: spectrum of CWISE J2035-4936 (black) compared to the spectral standards VB 8 (M7)(Kirkpatrick et al. 2010),VB 10 (M8)(Kirkpatrick et al. 2010), LHS 2924 (M9)(Kirkpatrick et al. 2010), 2MASS 0345+2540 (L0)(Kirkpatrick et al. 2010),and 2MASS 2130-0845 (L1)(Kirkpatrick et al. 2010). Right: CWISE J2035-4936 compared to LHS 377 (sdM7)(Gizis 1997;Greco et al. 2019), 2MASS 0142+0523 (sdM8.5)(Burgasser et al. 2007; Greco et al. 2019), SSSPM 1013 (sdM9.5)(Kirkpatricket al. 2014), and 2MASS 1756+2815 (sdL1)(Kirkpatrick et al. 2010; Greco et al. 2019), and SDSS J1256-0224 (sdL3.5)(Burgasseret al. 2009; Greco et al. 2019) All spectra were normalized between 1.27-1.29 microns and separated by a constant.
CatWISE 2020 proper motion for CWISE J2035-4936 is ( µ α , µ δ ) = ( − ± − ±
23) mas/yr, compared to ( µ α , µ δ ) = ( − ± − ± µm ) spectrum of CWISE J2035-4936 on UT 2019-06-19 using TripleSpec(Wilson et al. 2004) on the Southern Astrophysical Research (SOAR) Telescope. Using an ABBA nod pattern, weobserved a total of 12 exposures of 180 seconds each. Our science observations were taken at an airmass of 1.11”–1.17”under conditions of scattered high cirrus. Immediately following our observations of CWISE J2035-4936 we observedthe A0 star, HD 198546 (8 × µ α and µ δ both within ±
70 mas/yr of the corresponding CWISE J2035-4936 values (70 mas/yr ≈ × max[ σ µ α , σ µ δ ]). Given the angular separation of 34.2 (cid:48)(cid:48) , this yields a chance alignmentprobability of 1 . × − . The angular separation corresponds to a projected physical separation of ∼ Gaia
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