The following article is Open access

Spectroscopic Confirmation of the Nearby, Wide-separation L Dwarf Pair CWISE J061741.79+194512.8AB

, , , , , , , , , , , , , , , , and

Published August 2023 • © 2023. The Author(s). Published by the American Astronomical Society.
, , Citation Austin Humphreys et al 2023 Res. Notes AAS 7 184 DOI 10.3847/2515-5172/acf4a0

Article metrics

526 Total downloads

Share this article

Author affiliations

1 Department of Astronomy, University of Maryland, College Park, MD 20742, USA

2 NSF's National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA

3 Center for Astrophysics and Space Science, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA

4 Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman, Evanston, IL 60201, USA

5 United States Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Rd., Flagstaff, AZ 86005, USA

6 Department of Physics, Emory University, 201 Dowman Drive, Atlanta, GA 30322, USA

7 IPAC, Mail Code 100-22, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA

8 Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, NY 10024, USA

9 Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA

10 Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606, USA

Author notes

11 NASA Sagan Fellow.

ORCID iDs

Dates

  1. Received August 2023
  2. Accepted August 2023
  3. Published
Unified Astronomy Thesaurus concepts

Brown dwarfs; Low mass stars; Binary stars

Journal RSS
Create or edit your corridor alerts

What are corridors?opens in new tab

2515-5172/7/8/184

Abstract

We present spectroscopic confirmation of a nearby L dwarf pair, CWISE J061741.79+194512.8AB. Keck/NIRES near-infrared spectroscopy shows that the pair is composed of an L2 dwarf primary and an L4 dwarf secondary. High resolution spectroscopy of the combined light system with Keck/NIRSPEC yields a radial velocity of 29.2 ± 0.3 km s−1 and a projected rotational velocity $v\sin i\,$ = $\,{41.6}_{-2.6}^{+2.7}$ km s−1. Our spectrophotometric distance estimate places the system at 28.2 ± 5.7 pc, significantly more distant than originally estimated in Kirkpatrick et al. The angular separation of the components is 1farcs31 ± 0farcs14, corresponding to a projected physical separation of 37 ± 8 au.

Export citation and abstract BibTeX RIS

Previous article in issue
Next article in issue

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

1. Introduction

CWISE J061741.79+194512.8AB (hereafter J0617+1945AB) is a resolved ultracool dwarf binary system discovered through the Backyard Worlds citizen science project (Kuchner et al. 2017) and first announced by Kirkpatrick et al. (2021) as a candidate 20 pc census member. Initial analysis could only provide photometry-based estimates of the system's distance (∼7.5 pc) and spectral types (L6.5 primary, T8 secondary). Here, we present follow-up spectroscopy to further characterize this system.

2. Keck/NIRES Spectroscopy

Resolved spectroscopy of J0617+1945AB was obtained with the Near-Infrared Echellette Spectrometer (NIRES), a cross-dispersed, near-infrared spectrograph mounted on the Keck II 10 m telescope. Observations were obtained on 2021 January 2 (UT) in partly cloudy conditions with 0farcs8 seeing, with the NIRES slit aligned with the binary axis. Four 240 s exposures were acquired in an ABBA nodding pattern at an average airmass of 1.00. We also observed the A0 V HD 42198 at a similar airmass for flux calibration and telluric correction. Data were reduced using a modified version of Spextool (Vacca et al. 2003; Cushing et al. 2004).

Using the SpeX Prism Library Analysis Toolkit (SPLAT; Burgasser & the SPLAT Development Team 2017), we compared the reduced spectra for J0617+1945A and J0617+1945B against low-resolution SPLAT standards and NIRES standards from Theissen et al. (2022). We normalized all spectra at 1.27–1.29 μm, then compared them over the 1.0–1.4 μm range following Kirkpatrick et al. (2010), using the χ2 fitting statistic. The best-fitting standards were visually confirmed (Figure 1). We assign near-infrared classifications of L2 for J0617+1945A and L4 for J0617+1945B.

Figure 1.

Figure 1. Reduced Keck/NIRES spectra of J0617+1945A (top) and J0617+1945B (middle) with uncertainties in gray. Green curves show the corresponding smoothed NIRES standards (Theissen et al. 2022); blue curves show the corresponding low-resolution SPLAT standards (Burgasser 2007; Gagliuffi et al. 2014). Yellow shading indicates the region used for computing χ2. The bottom panel illustrates one of our best-fit NIRSPEC models. The NIRSPEC spectrum is shown in black and the best-fit forward models with/without telluric absorption are shown in blue and green, respectively, and residual (data-model) in magenta.

Download figure:

Standard image High-resolution image

3. Keck/NIRSPEC Spectroscopy

We obtained a high-resolution near-infrared spectrum of the combined J0617+1945AB system with the Near-Infrared Spectrometer (NIRSPEC), also mounted on the Keck II 10 m telescope. Data were obtained on 2021 October 23 (UT) in clear conditions and 0farcs55 seeing. We obtained 2 × 600 s exposures using a single AB nodding pair with the 0farcs432 ×12'' slit and NIRSPEC-7 order-sorting filter (λ/Δλ = 35,000). Our analysis focuses on order 33 data, spanning 2.29–2.33 μm. We also observed the B9V HD 198070 for telluric wavelength calibration, along with other standard calibration images. Data were reduced using a modified version of the NIRSPEC Data Reduction Pipeline (Tran et al. 2016; Hsu et al. 2021b). We obtained a combined median signal-to-noise of 19 per pixel.

To extract the stellar parameters of J0617+1945AB, we used the SMART package (Hsu et al. 2021a) for Markov Chain Monte Carlo forward-modeling. The bottom panel of Figure 1 shows the reduced and best-fit model spectra for J0617+1945AB.

4. Derived Quantities

4.1. Distance Estimates

2MASS J-band photometry for this system, J = 14.014 ± 0.031, reflects the combined light emission. We decomposed this into component magnitudes by estimating the relative brightnesses with the spectral type versus absolute JMKO magnitude relation from Kirkpatrick et al. (2021). We included a small ∼0.11 mag offset accounting for the difference between the JMKO and J2MASS filters. We determine component J2MASS magnitudes of J = 14.5 ± 0.3 for J0617+1945A and J = 15.1 ± 0.5 for J0617+1945B. We find a J-based spectrophotometric distance estimate of d = 28.2 ± 5.7 pc for J0617+1945AB.

We also attempted to measure the parallax of the combined light system from multi-epoch WISE data per Theissen (2018). We find π = 59 ± 11 mas, corresponding to a distance of ${16.9}_{-2.7}^{+3.9}$ pc, significantly nearer than our spectrophotometric distance. Our spectrophotometric distance is favored over the trigonometric distance due to the Lutz-Kelker bias affecting low signal-to-noise parallaxes (Lutz & Kelker 1973).

4.2. Kinematics

CatWISE2020 provides J0617+1945AB proper motions of ${\mu }_{\alpha }\cos \delta =-107.9\pm 4.0$ mas yr−1, μδ  = − 57.9 ± 3.8 mas yr−1, and μtotal = 122.5 ± 4.0 mas yr−1 (found via VizieR). Adopting our spectrophotometric distance, this proper motion implies a tangential velocity of 16.4 ± 3.4 km s−1. From the NIRSPEC spectra, we obtain a heliocentric radial velocity of 29.2 ± 0.3 km s−1 and a projected rotational velocity $v\sin i\,$ = $\,{41.6}_{-2.6}^{+2.7}$ km s−1. Combing our radial velocity, proper motions, and distance, we computed an LSR-corrected UVW velocity of (U, V, W) = (−18.2 ± 0.3, 7.0 ± 0.5, −9.4 ± 2.3) km s−1 and found that J0617+1945AB is a field ultracool dwarf binary system (>99% probability) using BANYAN Σ (Gagné et al. 2018).

4.3. Physical Properties

Reanalyzing semi-resolved UKIDSS imaging, we find an angular separation of θ = 1farcs31 ± 0farcs14, and thus a projected physical separation of 37 ± 8 au. From the NIRSPEC spectra, we find a (combined light) effective temperature ${T}_{\mathrm{eff}}={1853}_{-52}^{+40}$ K, and a (combined light) surface gravity $\mathrm{log}g\,$ = 4.78 ${}_{-0.12}^{+0.11}$ dex. This temperature corresponds to an infrared spectral type of ${\rm{L}}{2.9}_{-0.4}^{+0.3}$, consistent with the blended spectrum of L2 and L4 components.

5. Discussion

We conclude that J0617+1945AB is an L2+L4 ultracool dwarf pair significantly more distant than originally estimated. J0617+1945AB joins a small but growing sample of field age binaries with L-type (or later) components and separations greater than a few dozen au (e.g., Softich et al. 2022).

Acknowledgments

This work has been supported in part by the NASA Citizen Science Seed Funding Program, grant 80NSSC21K1485. This material is based upon work supported by the National Science Foundation under grant Nos. 2007068, 2009136, and 2009177.

Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Please wait… references are loading.
10.3847/2515-5172/acf4a0