Discovery of 34 Low-mass Comoving Systems Using NOIRLab Source Catalog DR2

Binary and multiple stellar systems have long been used to study the formation and fundamental properties of stars. With the first discovery of brown dwarf binary systems (Martín et al. 1998; Basri & Martín 1999; Martín et al. 1999), these investigations have been extended into the substellar regime. Physical properties of individual brown dwarfs (e.g., mass, metallicity, or surface gravity) are difficult to determine due to the absence of main-sequence hydrogen burning, causing them to cool and fade over time. For brown dwarfs in multiple systems, however, physical properties, age, and composition can be inferred from their stellar companions. Further, the binary fraction, mass ratio distribution, and separation of brown dwarf companion systems can provide constraints on star formation and dynamical evolution (Goodwin & Whitworth 2007).

A valuable type of benchmark system is one with a wide binary composed of resolved companions, the primary being a main-sequence star and the secondary being an L or T dwarf. Because it is very difficult to determine properties such as metallicity and age of L and T dwarfs, these properties can be inferred from the primary since comoving systems are assumed to have formed at the same time from the same material, and developed in the same environment. However, benchmark systems involving L or T dwarf companions are more difficult to find than systems composed of earlier type companions, because often either the primary is saturated or the secondary remains undetected. Moreover, the binary fraction seems to decrease from early to late primary spectral types (Kraus & Hillenbrand 2012). While the binary fraction for solar-type stars ranges within 50%–60% (Duquennoy & Mayor 1991; Raghavan et al. 2010), it decreases to 30%–40% for M stars (Fischer & Marcy 1992; Delfosse et al. 2004; Janson et al. 2014; Winters et al. 2019). For field brown dwarfs, the resolved binary fraction for very low-mass systems is around 10%–20% (Close et al. 2003; Burgasser et al. 2006; Gelino et al. 2011; Huélamo et al. 2015; Fontanive et al. 2018).

Identifying comoving companions has become easier through the use of large, multiepoch surveys such as the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010), the Gaia Mission (Gaia Collaboration et al. 2016), or the DESI Legacy Imaging Surveys (Dey et al. 2019). Resulting catalogs like CatWISE2020 (Marocco et al. 2021), Gaia DR2 (Gaia Collaboration et al. 2018), Gaia EDR3 (Gaia Collaboration et al. 2021) or NSC DR2 (Nidever et al. 2021) are excellent resources for finding late-type moving objects and their potential companions by using the provided proper motions. Two objects sufficiently close to each other on the sky and having comparable proper motions can provide a basis for inferring a common origin.

This paper is outlined as follows. In Section 2, we briefly describe the NSC and its key elements relevant to this work. In Section 3, we present our search method, and in Section 4, we characterize the discovered systems. We discuss some of the systems in more detail in Section 5.

NSC DR2 (Nidever et al. 2021) is based on public image data from the NOIRLab Astro Data Archive. These images come from telescopes in both hemispheres (CTIO − 4 m + DECam, KPNO − 4 m + Mosaic3, and Bok − 2.3 m + 90'') and cover ∼35,000 square degrees of the sky. A significant part of the images was obtained by the Dark Energy Survey (DES; Abbott et al. 2018) and the DESI Legacy Imaging Surveys (Dey et al. 2019). NSC DR2 includes more than 3.9 billion single objects with over 68 billion individual source measurements. It has depths of ∼ 23rd mag in most broadband filters (u, g, r, i, z, Y, and VR), accurate proper motions, and an astrometric accuracy of ∼7 mas.

NSC provides proper motion measurements that push much fainter at optical wavelengths than Gaia DR2 or EDR3. At g band, NSC is ∼2.5 mag deeper than Gaia and allows proper motion searches for distant stars with high tangential velocities over a volume ∼25 times larger than Gaia. NSC can also measure motions for white dwarfs much fainter than those detected by Gaia, expanding the census of white dwarfs in the solar neighborhood. NSC's accurate proper motions enable the discovery of ultracool white dwarf binaries where metallicity and radial velocity can be derived from a main-sequence companion (Lam et al. 2020).

Due to its excellent red-optical sensitivity and sky coverage, NSC provides many new possibilities to search for ultracool stars and brown dwarfs in the solar neighborhood. CatWISE2020 (Marocco et al. 2021) represents one of the best infrared proper motion catalogs currently available. However, at its faint end, CatWISE motions are only significant above ∼150–200 mas yr⁻¹, unlike NSC, which can measure motions many times smaller at high significance. NSC's Y-band depth (23.4 mag) and angular resolution (∼1'') allow for motion searches of late-type objects not possible with WISE. This enables queries for pairs of faint objects with consistent proper motions to find closely spaced low-mass companion systems.

In a first step, we searched for previously missed L and T dwarfs in the NOIRLab Source Catalog using proper motion and photometry. We used the z, i, and Y magnitudes along with the relations described in Carnero Rosell et al. (2019) to determine the color cut for our initial selection. We required all objects to have at least one detection in each of those three bands. The adopted color cut (1.4 < (i − z)_NSC < 3.5 and 0.4 < (z − Y)_NSC < 1.5) should restrict the search to L and T dwarfs. However, it cannot be excluded that some late M dwarfs are within the selected objects. Note that both color constraints had to be satisfied for this selection. No quality cuts were applied to the photometry to avoid eliminating more distant late-type/faint objects with less accurate photometry. Candidates having proper motions below 100 mas yr⁻¹ have been discarded from the selection to provide proper motions significant enough to be visually confirmed by blinking images of different epochs. We avoided the galactic plane (∣b∣ > 15°) to further reduce the number of sources with spurious proper motions. We required a high star–galaxy classifier of at least 0.7 to ensure that the search only returns objects with a point-like morphology. The star–galaxy classifier is an NSC catalog column that provides information on an object's probability of being either a galaxy or a star, based on its morphology. Selected objects had to have a time baseline of at least 6 months between the first and last observation. By applying these criteria, we obtained a total of 2896 candidate ultracool dwarfs, mostly in the L and T regimes.

In a second step, we examined a 100'' radius around all 2896 objects using the NSC by comparing the proper motion components of each object to the proper motion components of the objects found in the defined radius. We applied a proper motion matching tolerance of 20 mas yr⁻¹ to find potential companions either of earlier or later type. Note that we exclusively used NSC DR2 proper motions for this purpose. As in the first step, we excluded objects having a star–galaxy classifier below 0.7 and a time baseline of fewer than 6 months. To further reduce the number of false positives, each identified companion was cross-matched with Gaia EDR3 to discard objects with a parallax below 2 mas. This resulted in 46 pairs with similar proper motions.

Among those 46 potential companions, we found four false positives (no object visible in WISE or DECaLS imagery), three likely false positives with significant differences in their proper motion components, and thirteen known pairs, one of which (NSC J2322−6151) is referenced in Smart et al. (2019) and Calissendorff et al. (2019), the other 12 find mention in the SUPERWIDE catalog (Hartman & Lépine 2020). The known pairs, which are listed in Table 1 (Rediscovered Systems), are not further described in this paper.

Table 1. Discovered Systems

Sys.	System Name	Short Name	ϖ	μα	μδ	Dist. a	${\upsilon }_{\tan }$ b	Sep. c	Sep. d	Pos. e	Sys. f	References g
#			(mas)	(mas yr−1)	(mas yr−1)	(pc)	(km s−1)	('')	(AU)	(deg)	type
	Newly Discovered Systems
1	NSC J000456.31+045117.22 AB	NSC J0004+0451	9.2747 ± 0.1585	100.538 ± 0.206	10.524 ± 0.146	107.821 ± 1.843	51.663 ± 0.889	14.548	1568.531	15.4	M6 + L2	⋯
2	NSC J004058.68−294212.37 AB	NSC J0040−2942	18.1726 ± 0.1292	84.313 ± 0.128	−124.955 ± 0.143	55.028 ± 0.391	39.318 ± 0.282	19.906	1095.379	181.2	M7 + T5	⋯
3	NSC J004239.82−250714.01 AB	NSC J0042−2507	3.8355 ± 0.8464	109.022 ± 0.936	−17.709 ± 0.846	260.725 ± 57.535	136.499 ± 30.144	3.000	782.216	237.1	M6 + M6	⋯
4	NSC J004509.91−285557.20 AB	NSC J0045−2855	6.8596 ± 0.0544	93.307 ± 0.055	−24.9 ± 0.061	145.78 ± 1.156	66.732 ± 0.531	5.447	794.110	286.4	M4 + M9	⋯
5	NSC J010717.67−265848.32 AB	NSC J0107−2658	11.5915 ± 0.0202	115.191 ± 0.021	−119.037 ± 0.027	86.27 ± 0.15	67.736 ± 0.118	5.846	504.352	333.8	M1 + M8	⋯
6	NSC J012629.63−262023.18 AB	NSC J0126−2620	6.8549 ± 0.0307	101.256 ± 0.04	−51.201 ± 0.027	145.882 ± 0.653	78.459 ± 0.352	7.921	1155.583	215.7	M3 + M8	⋯
7	NSC J014827.71−035716.63 AB	NSC J0148−0357	8.4201 ± 0.0628	52.933 ± 0.081	−175.686 ± 0.042	118.764 ± 0.886	103.292 ± 0.771	11.752	1395.736	131.3	M4 + L4	⋯
8	NSC J015340.10−001550.34 AB	NSC J0153−0015	5.4188 ± 0.0236	83.398 ± 0.029	−105.841 ± 0.02	184.544 ± 0.804	117.871 ± 0.514	4.206	776.150	359.0	M1 + M8	⋯
9	NSC J020029.71−125451.00 AB	NSC J0200−1254	4.3019 ± 0.0211	146.841 ± 0.021	−84.873 ± 0.018	232.455 ± 1.14	186.876 ± 0.917	36.509	8486.735	260.8	K7 + L9	⋯
10	NSC J020048.45−470755.84 AB	NSC J0200−4707	13.2326 ± 0.0145	107.904 ± 0.013	−4.801 ± 0.014	75.571 ± 0.083	38.69 ± 0.043	22.380	1691.254	213.5	M2 + L4	⋯
11	NSC J020541.24+020249.66 AB	NSC J0205+0202	8.7286 ± 0.736	−81.262 ± 0.898	−73.003 ± 0.67	114.566 ± 9.66	59.321 ± 5.021	5.561	637.127	95.9	M7 + L8	⋯
12	NSC J022132.42−633807.41 AB	NSC J0221−6338	6.4144 ± 0.1885	101.832 ± 0.25	43.48 ± 0.237	155.9 ± 4.581	81.823 ± 2.411	37.757	5886.303	140.4	M6 + L1	⋯
13	NSC J022821.48−532004.36 AB	NSC J0228−5320	10.8681 ± 0.0441	127.645 ± 0.045	27.171 ± 0.049	92.012 ± 0.373	56.918 ± 0.232	5.962	548.533	185.2	M3 + M8	⋯
14	NSC J023113.30−031147.09 AB	NSC J0231−0311	12.3836 ± 0.2079	24.676 ± 0.236	−128.072 ± 0.195	80.752 ± 1.356	49.923 ± 0.841	5.246	423.614	341.3	M7 + L4	⋯
15	NSC J024433.27−051711.10 AB	NSC J0244−0517	3.8755 ± 0.0509	27.951 ± 0.051	−104.003 ± 0.049	258.033 ± 3.389	131.717 ± 1.731	3.905	1007.524	265.6	M1 + L0	⋯
16	NSC J024507.25−123726.57 AB	NSC J0245−1237	6.0612 ± 0.0295	34.715 ± 0.033	−141.047 ± 0.034	164.983 ± 0.803	113.593 ± 0.554	5.808	958.154	234.1	M2 + M7	⋯
17	NSC J025450.03−085252.25 AB	NSC J0254−0852	8.2213 ± 0.0638	115.448 ± 0.078	−48.647 ± 0.064	121.635 ± 0.944	72.23 ± 0.562	6.095	741.364	14.9	M3 + L0	⋯
18	NSC J041239.68−262105.02 AB	NSC J0412−2621	6.3603 ± 0.24	−10.497 ± 0.189	−164.793 ± 0.27	157.225 ± 5.933	123.06 ± 4.648	2.617	411.436	36.3	M6 + M8	⋯
19	NSC J041641.96−215248.86 AB	NSC J0416−2152	7.4598 ± 0.0326	117.348 ± 0.027	−219.012 ± 0.032	134.052 ± 0.586	157.878 ± 0.69	8.411	1127.526	306.3	M3 + M9	⋯
20	NSC J043503.99−355911.42 AB	NSC J0435−3559	9.3695 ± 0.0287	−8.94 ± 0.027	−96.481 ± 0.034	106.729 ± 0.327	49.018 ± 0.151	23.948	2555.901	299.7	M4 + L5	⋯
21	NSC J045724.25−230012.74 AB	NSC J0457−2300	18.187 ± 0.0217	−128.657 ± 0.015	7.236 ± 0.02	54.984 ± 0.066	33.584 ± 0.04	16.970	933.096	317.3	M4 + T3	⋯
22	NSC J050456.74−482240.01 AB	NSC J0504−4822	12.574 ± 0.0199	−3.188 ± 0.023	132.932 ± 0.029	79.529 ± 0.126	50.126 ± 0.08	7.175	570.648	248.1	M3 + L0	⋯
23	NSC J050506.28−475035.19 AB	NSC J0505−4750	6.3997 ± 0.1196	70.225 ± 0.131	88.813 ± 0.184	156.256 ± 2.92	83.858 ± 1.572	7.787	1216.806	208.4	M6 + M9	⋯
24	NSC J052307.20−565522.36 AB	NSC J0523−5655	18.3926 ± 0.0234	−28.942 ± 0.029	156.764 ± 0.029	54.37 ± 0.069	41.083 ± 0.053	12.995	706.547	333.2	M5 + T0	⋯
25	NSC J053232.31−512450.75 AB	NSC J0532−5124	5.9143 ± 0.3818	102.804 ± 0.432	138.888 ± 0.479	169.081 ± 10.915	138.487 ± 8.948	3.003	507.731	80.4	WD + L3	⋯
26	NSC J123900.73−005433.72 AB	NSC J1239−0054	23.3826 ± 0.0281	−103.965 ± 0.036	−47.8 ± 0.032	42.767 ± 0.051	23.196 ± 0.029	8.817	377.062	39.8	M4 + L4	⋯
27	NSC J130527.23−224728.44 AB	NSC J1305−2247	6.9608 ± 0.7951	−140.208 ± 1.111	2.719 ± 0.754	143.661 ± 16.41	95.493 ± 10.934	4.983	715.907	358.1	WD + L3	⋯
28	NSC J132017.47−401258.27 AB	NSC J1320−4012	14.9605 ± 0.0182	−17.48 ± 0.016	−117.831 ± 0.016	66.843 ± 0.081	37.742 ± 0.046	55.312	3697.213	300.0	M1 + L1	⋯
29	NSC J202349.63−484435.01 AB	NSC J2023−4844	10.4053 ± 0.0331	13.143 ± 0.032	−132.182 ± 0.028	96.105 ± 0.306	60.511 ± 0.193	11.382	1093.871	225.4	M4 + L0	⋯
30	NSC J220852.71−551054.25 AB	NSC J2208−5510	10.4478 ± 0.0612	−136.283 ± 0.061	5 ± 0.055	95.714 ± 0.561	61.871 ± 0.363	4.498	430.541	113.1	M5 + M9	⋯
31	NSC J224101.90−450026.44 AB	NSC J2241−4500	17.1738 ± 0.6061	273.035 ± 0.404	−154.157 ± 0.509	58.228 ± 2.055	86.54 ± 3.057	7.183	418.277	144.5	M5 + L2	⋯
32	NSC J232703.65−524727.94 AB	NSC J2327−5247	8.6324 ± 0.0161	108.844 ± 0.013	−32.352 ± 0.016	115.842 ± 0.216	62.349 ± 0.117	56.005	6487.802	243.5	M1 + L1	⋯
33	NSC J233302.51−634721.39 AB	NSC J2333−6347	8.8339 ± 0.4268	48.71 ± 0.376	−162.431 ± 0.422	113.2 ± 5.469	90.99 ± 4.402	2.851	322.740	26.5	WD + M9	⋯
34	NSC J234443.91+003112.41 AB	NSC J2344+0031	8.1622 ± 0.175	−92.89 ± 0.188	−103.067 ± 0.127	122.516 ± 2.627	80.575 ± 1.73	8.414	1030.796	270.9	M6 + L2	⋯
	Rediscovered Systems
⋯	NSC J002111.11−424540.39 AB	NSC J0021−4245	37.3319 ± 0.0378	255.184 ± 0.031	−12.475 ± 0.039	26.787 ± 0.027	32.439 ± 0.033	77.840	2085.087	316.9	M6 + L0	1
⋯	NSC J003011.68−374049.20 AB	NSC J0030−3740	21.0552 ± 0.0576	−86.91 ± 0.042	−65.42 ± 0.059	47.494 ± 0.13	24.489 ± 0.068	89.057	4229.675	312.3	WD + M9	1
⋯	NSC J003320.53−422726.41 AB	NSC J0033−4227	16.4251 ± 0.0183	320.573 ± 0.015	−46.16 ± 0.014	60.883 ± 0.068	93.466 ± 0.104	29.065	1769.531	125.2	M3 + L0	1
⋯	NSC J013609.18−255613.81 AB	NSC J0136−2556	13.7237 ± 0.1623	203.037 ± 0.184	17.952 ± 0.095	72.867 ± 0.862	70.4 ± 0.835	7.074	515.438	34.5	WD + L0	1
⋯	NSC J014953.56−612919.67 AB	NSC J0149−6129	13.0666 ± 0.0544	3.697 ± 0.06	−161.535 ± 0.063	76.531 ± 0.319	58.613 ± 0.245	12.321	942.972	338.5	WD + L0	1
⋯	NSC J020640.61−222439.29 AB	NSC J0206−2224	7.525 ± 0.0578	88.629 ± 0.049	−61.198 ± 0.045	132.89 ± 1.021	67.843 ± 0.522	9.978	1325.982	336.8	M3 + M7	1
⋯	NSC J023508.17−041443.11 AB	NSC J0235−0414	17.7429 ± 0.0284	114.207 ± 0.032	−22.807 ± 0.029	56.36 ± 0.09	31.113 ± 0.051	11.587	653.049	340.0	M4 + M9	1
⋯	NSC J044142.59−304256.75 AB	NSC J0441−3042	14.7129 ± 0.0408	63.624 ± 0.038	83.713 ± 0.045	67.968 ± 0.188	33.875 ± 0.095	17.664	1200.582	53.6	M5 + M9	1
⋯	NSC J124428.51−011900.40 AB	NSC J1244−0119	12.0087 ± 0.0502	−57.115 ± 0.066	−171.286 ± 0.047	83.273 ± 0.348	71.269 ± 0.299	3.080	256.494	252.4	WD + M9	1
⋯	NSC J203439.06−541247.73 AB	NSC J2034−5412	9.3785 ± 0.0857	3.973 ± 0.078	−105.771 ± 0.083	106.626 ± 0.974	53.495 ± 0.491	30.371	3238.356	212.2	M5 + M9	1
⋯	NSC J211810.50−472110.21 AB	NSC J2118−4721	15.117 ± 0.0219	153.639 ± 0.02	−216.018 ± 0.016	66.151 ± 0.096	83.118 ± 0.121	3.333	220.509	176.7	M3 + M9	1
⋯	NSC J232028.36−495545.70 AB	NSC J2320−4955	13.1006 ± 0.1154	75.9 ± 0.081	−75.051 ± 0.09	76.332 ± 0.672	38.62 ± 0.342	7.363	562.070	2.7	M7 + M8	1
⋯	NSC J232252.60−615112.77 AB	NSC J2322−6151	23.5626 ± 0.0296	78.122 ± 0.028	−78.252 ± 0.033	42.44 ± 0.053	22.244 ± 0.029	16.589	704.027	165.6	M5 + L2	2,3

Notes. The parallaxes and proper motions are from Gaia EDR3. The primary of system #8 and the secondary of system #21 have confirmed spectral types of M0 and T3, respectively (see the spectra in Figure 4).

^a Distance, derived from the Gaia EDR3 parallax of the primary. ^b Tangential velocity, calculated using the Gaia EDR3 astrometry of the primary. ^c Angular separation. ^d Projected physical separation, calculated using the Gaia EDR3 parallax of the primary. ^e Position angle (east of north) of the secondary with respect to the primary. ^f System type, based on spectral type estimates (A + B). ^g Binary system references: (1) Hartman & Lépine (2020), (2) Smart et al. (2019), (3) Calissendorff et al. (2019) ^(c,e) Calculated using NSC DR2 positions, translating the position of the primary to the epoch of the secondary.

Download table as:  ASCIITypeset images: 1 2 3

We repeated both steps described above using a slightly different color cut than in the first selection (i_NSC > 99 and 0.4 < (z − Y)_NSC < 1.5). The goal of this second selection was to target specifically substellar sources and not more distant warmer stars. Since late-type brown dwarfs emit more radiation in the near-infrared, an i-band dropout is a strong signature for detecting a cold compact source. We therefore dropped the i − z color but used the same constraints for the z − Y color as in the first selection. We also required selected objects explicitly to have no i-band photometry by adding a corresponding constraint (i > 99) to exclude any objects found in the first selection. After applying the first step of our search method, we obtained a total of 2520 objects. Step two resulted in three additional systems, #2, #21, and #24, having secondaries with estimated spectral types of T5, T3, and T0, respectively.

Each object has been visually inspected to determine whether its proper motion components are consistent with those of its comoving companion by blinking images of different epochs. For this, we used AstroToolBox (Kiwy 2022), which is a Java tool set with a graphical user interface allowing us to blink either unWISE coadds (Meisner et al. 2017, 2018) of epochs 2010 and 2014–2020, or DECaLS cutouts (Dey et al. 2019) from DR5, DR7, DR8, and DR9. DECaLS cutouts have a resolution 10 × higher than unWISE coadds (027 pixel⁻¹ versus 275 pixel⁻¹), making it possible to identify the components of binary systems down to an angular separation of ∼ 1''. All objects have been carefully checked against at least one background star, showing no visible motion, to eliminate false positives produced by misaligned images.

To assess the effect of the photometric uncertainties on the selection, we calculated the mean photometric error associated with the (i − z)_NSC and (z − Y)_NSC colors of the secondaries in our sample, which is 0.035 mag for both of these colors (Table 8). The used color cut (1.4 < i − z < 3.5 and 0.4 < z − Y < 1.5) was determined by means of the Carnero Rosell et al. (2019) relations with the following color values for the given spectral types: {L0, T9}={(i − z = 1.48, z − Y =0.43), (i − z = 3.39, z − Y = 1.5)}. Note that the Carnero Rosell relations do not give uncertainties on their color values. When we subtract the mean photometric errors from the color values for spectral type L0, we obtain the following values: i − z = 1.48 − 0.035 = 1.445 and z − Y = 0.43 −0.035 =0.395. While the value for the i − z color is still above the lower limit of our color cut, that for the z − Y color is 0.005 mag below the limit. Given this small color value difference, we conclude that it has a minimal, if any, effect on the selection. As for the upper limits of the used color cut, the photometric errors do not affect the selection since our sample does not contain objects with estimated spectral types later than T5. This corresponds to the color values i − z = 3.25 and z − Y = 1.02 from the Carnero Rosell relations, which both are well below the upper bounds of the employed color cut (i − z = 3.5, z − Y = 1.5), and stay well below even if we add the mean photometric uncertainties (i − z = 3.25 + 0.035 =3.285 and z − Y = 1.02 + 0.035 = 1.055).

Aside from the 29 new systems discovered through the method described above, an additional five new systems (#3, #11, #16, #25, and #27) were recovered serendipitously when visually checking a list of objects from a previous NSC DR2 search focused on high proper motion ultracool dwarf candidates. The color and proper motion cuts used in that search were somewhat different from those applied in step one of this work. In each of these cases, the companion could be identified through AstroToolBox's image blinker. For those five systems, either the primary or the secondary did not satisfy all the constraints defined in the search method of this work.

At the same time these searches were ongoing, several members of the Backyard Worlds: Planet 9 citizen science project (Kuchner et al. 2017) were searching for similar cold compact objects via the Zooniverse portal or via a research scientist guided side project. Arttu Sainio recovered system #21, Vinod Thakur recovered systems #13 and #20, and Sam Goodman recovered systems #1 and #35. Details on those searches and additional discoveries by the larger Backyard Worlds team will be reported in a forthcoming paper.

We identified a total of 34 new candidate binary systems, most of which are located in the DES footprint ¹³ (Abbott et al. 2021). The general properties of these systems are given in Table 1 (Newly Discovered Systems) with additional astrometry from NSC DR2 in Table 2 and relevant photometry in Table 7. Histograms showing the distribution of distances, angular and physical separations, total proper motions, and tangential velocities can be found in Figure 2.

Table 2. NSC DR2 Astrometry

Sys.	C. a	α	δ	Epoch	μα	μδ	μtot	Δμα b	Δμδ c	Δμtot d
#		(deg)	(deg)		(mas yr−1)	(mas yr−1)	(mas yr−1)	(mas yr−1)	(mas yr−1)	(mas yr−1)
1	A	1.2346196 ± 0002078	4.8547833 ± 0002548	2017-02-17	101.586 ± 2.081	16.224 ± 2.243	102.873 ± 2.085
	B	1.2356978 ± 0008701	4.8586783 ± 0008999	2017-01-31	103.442 ± 10.176	8.665 ± 10.271	103.804 ± 10.177	1.856 ± 10.387	7.559 ± 10.513	7.784 ± 10.506
2	A	10.2445114 ± 0002146	−29.703435 ± 0002093	2016-09-23	85.588 ± 1.684	−127.509 ± 1.637	153.57 ± 1.652
	B	10.2443636 ± 0015625	−29.7089511 ± 0015601	2016-05-22	76.615 ± 11.596	−137.72 ± 11.576	157.596 ± 11.581	8.973 ± 11.718	10.211 ± 11.691	13.593 ± 11.703
3	A	10.6659165 ± 0002078	−25.1205574 ± 0002254	2017-06-23	110.017 ± 1.081	−18.631 ± 1.168	111.583 ± 1.084
	B	10.6651479 ± 0002717	−25.1210108 ± 0002906	2017-08-07	114.399 ± 1.451	−16.276 ± 1.542	115.551 ± 1.453	4.382 ± 1.809	2.355 ± 1.934	4.975 ± 1.838
4	A	11.2912826 ± 0002091	−28.9325546 ± 0002165	2016-10-10	91.114 ± 1.456	−24.391 ± 1.525	94.322 ± 1.461
	B	11.2896207 ± 0002027	−28.9321265 ± 0002127	2016-08-29	98.791 ± 1.421	−25.35 ± 1.474	101.992 ± 1.424	7.677 ± 2.034	0.959 ± 2.121	7.737 ± 2.036
5	A	16.8236365 ± 0010278	−26.9800885 ± 0008563	2017-02-24	120.909 ± 13.555	−114.787 ± 11.718	166.718 ± 12.717
	B	16.822841 ± 0003846	−26.978638 ± 0003594	2017-05-15	123.797 ± 3.129	−132.236 ± 2.945	181.141 ± 3.032	2.888 ± 13.911	17.449 ± 12.082	17.686 ± 12.135
6	A	21.6234552 ± 0003409	−26.3397711 ± 0003143	2015-08-16	94.787 ± 4.24	−53.296 ± 3.25	108.743 ± 4.024
	B	21.6220425 ± 0004235	−26.341568 ± 000456	2016-04-26	104.433 ± 2.991	−39.322 ± 3.367	111.591 ± 3.04	9.646 ± 5.189	13.974 ± 4.68	16.98 ± 4.85
7	A	27.1154771 ± 0002914	−3.9546199 ± 0002943	2016-02-23	49.302 ± 1.912	−171.409 ± 2.122	178.358 ± 2.107
	B	27.1179324 ± 0023287	−3.9567589 ± 0023424	2015-11-05	68.828 ± 16.381	−168.594 ± 16.504	182.102 ± 16.486	19.526 ± 16.492	2.815 ± 16.64	19.728 ± 16.495
8	A	28.4171021 ± 0004829	−0.2639823 ± 0006201	2015-02-22	85.484 ± 2.781	−109.777 ± 4.129	139.135 ± 3.679
	B	28.4171034 ± 0004138	−0.2628419 ± 0004276	2016-01-19	85.823 ± 2.704	−110.007 ± 2.7	139.525 ± 2.702	0.339 ± 3.879	0.23 ± 4.933	0.41 ± 4.24
9	A	30.1238025 ± 0004582	−12.9141655 ± 0004964	2015-10-30	146.547 ± 4.654	−85.844 ± 4.933	169.839 ± 4.727
	B	30.1135648 ± 0017378	−12.9158077 ± 0017444	2016-08-11	163.476 ± 11.532	−85.838 ± 11.596	184.642 ± 11.546	16.929 ± 12.436	0.006 ± 12.602	16.929 ± 12.436
10	A	30.2018838 ± 0006962	−47.1321787 ± 0005139	2015-03-28	108.767 ± 3.213	−5.923 ± 2.803	108.928 ± 3.212
	B	30.1968786 ± 0012833	−47.1373651 ± 001282	2016-01-17	109.414 ± 7.503	−7.568 ± 7.513	109.675 ± 7.503	0.647 ± 8.162	1.645 ± 8.019	1.768 ± 8.038
11	A	31.421821 ± 0003174	2.0471276 ± 0003597	2016-02-05	−79.908 ± 1.652	−72.908 ± 1.83	108.171 ± 1.735
	B	31.4233605 ± 0048468	2.0469716 ± 0048787	2016-01-06	−79.81 ± 27.969	−79.694 ± 28.054	112.786 ± 28.011	0.098 ± 28.018	6.786 ± 28.114	6.787 ± 28.114
12	A	35.3850943 ± 0002373	−63.635391 ± 0002409	2016-05-01	99.186 ± 1.589	40.524 ± 1.59	107.145 ± 1.589
	B	35.4001583 ± 0011979	−63.6434698 ± 0012019	2016-05-15	94.643 ± 7.404	57.983 ± 7.437	110.992 ± 7.413	4.543 ± 7.573	17.459 ± 7.605	18.04 ± 7.603
13	A	37.0895103 ± 0005066	−53.3345431 ± 0004095	2015-08-01	128.523 ± 2.28	25.6 ± 2.016	131.048 ± 2.27
	B	37.0892954 ± 0003524	−53.3361878 ± 0003471	2016-03-18	135.364 ± 1.736	44.364 ± 1.681	142.449 ± 1.731	6.841 ± 2.866	18.764 ± 2.625	19.972 ± 2.654
14	A	37.8054288 ± 000155	−3.1964142 ± 000168	2014-10-19	27.345 ± 0.764	−126.129 ± 0.875	129.059 ± 0.87
	B	37.8049613 ± 0019263	−3.195033 ± 0019493	2014-10-12	23.43 ± 8.058	−122.34 ± 8.252	124.563 ± 8.245	3.915 ± 8.094	3.789 ± 8.298	5.448 ± 8.193
15	A	41.1386057 ± 0002152	−5.2864157 ± 0002432	2015-12-06	28.081 ± 1.252	−103.368 ± 1.425	107.114 ± 1.414
	B	41.1375166 ± 0009645	−5.2864883 ± 0009866	2015-07-16	33.115 ± 5.409	−95.38 ± 5.519	100.965 ± 5.507	5.034 ± 5.552	7.988 ± 5.7	9.442 ± 5.658
16	A	41.2802081 ± 0003752	−12.624046 ± 0003647	2015-11-18	31.967 ± 3.213	−142.653 ± 3.03	146.191 ± 3.039
	B	41.2788699 ± 0003593	−12.6249969 ± 0003506	2016-01-07	35.216 ± 2.566	−139.192 ± 2.569	143.578 ± 2.569	3.249 ± 4.112	3.461 ± 3.972	4.747 ± 4.038
17	A	43.7084538 ± 0002476	−8.8811802 ± 0002285	2016-04-25	117.81 ± 1.636	−47.432 ± 1.418	127 ± 1.607
	B	43.7088891 ± 0005807	−8.8795421 ± 0005976	2016-03-04	122.706 ± 4.318	−50.082 ± 4.482	132.533 ± 4.342	4.896 ± 4.618	2.65 ± 4.701	5.567 ± 4.637
18	A	63.1653339 ± 000273	−26.3513948 ± 0002554	2016-02-12	−11.367 ± 1.854	−171.564 ± 1.774	171.94 ± 1.774
	B	63.1658141 ± 0006391	−26.3508035 ± 0006278	2016-01-03	−21.539 ± 4.404	−165.401 ± 4.288	166.798 ± 4.29	10.172 ± 4.778	6.163 ± 4.64	11.893 ± 4.742
19	A	64.1748361 ± 0005138	−21.8802396 ± 0004524	2017-10-14	126.736 ± 6.728	−211.923 ± 5.893	246.928 ± 6.124
	B	64.1727738 ± 0004377	−21.8788069 ± 0004248	2016-12-06	116.722 ± 3.622	−223.551 ± 3.549	252.189 ± 3.565	10.014 ± 7.641	11.628 ± 6.879	15.346 ± 7.213
20	A	68.7666169 ± 0004239	−35.9865056 ± 0003406	2015-09-16	−7.196 ± 3.604	−99.253 ± 3.035	99.514 ± 3.038
	B	68.7594779 ± 0018314	−35.9832042 ± 0018233	2015-08-06	−19.485 ± 11.443	−100.729 ± 11.386	102.596 ± 11.388	12.289 ± 11.997	1.476 ± 11.784	12.377 ± 11.994
21	A	74.3510223 ± 0003104	−23.0035376 ± 0003016	2016-12-31	−122.647 ± 2.746	3.851 ± 2.62	122.707 ± 2.746
	B	74.3475712 ± 0009615	−23.0000735 ± 0009499	2016-06-02	−117.71 ± 7.21	8.87 ± 7.089	118.044 ± 7.209	4.937 ± 7.715	5.019 ± 7.558	7.04 ± 7.636
22	A	76.2364019 ± 0004426	−48.3777799 ± 0003606	2015-02-28	−6.873 ± 2.628	131.213 ± 2.716	131.393 ± 2.716
	B	76.2336175 ± 0004861	−48.3785139 ± 0004749	2015-06-14	−3.561 ± 3.02	129.436 ± 3.031	129.485 ± 3.031	3.312 ± 4.003	1.777 ± 4.07	3.759 ± 4.018
23	A	76.2761717 ± 0002213	−47.8431073 ± 0002096	2014-07-23	71.531 ± 1.131	89.929 ± 1.069	114.908 ± 1.093
	B	76.2746353 ± 0003374	−47.8450102 ± 0003375	2014-07-09	72.705 ± 1.733	88.922 ± 1.709	114.861 ± 1.719	1.174 ± 2.069	1.007 ± 2.016	1.547 ± 2.047
24	A	80.7800047 ± 0003103	−56.9228765 ± 0003141	2013-05-15	−20.786 ± 7.213	160.34 ± 7.203	161.682 ± 7.203
	B	80.7770104 ± 0017716	−56.9196198 ± 0017769	2014-03-04	−33.032 ± 9.194	160.116 ± 9.229	163.488 ± 9.228	12.246 ± 11.686	0.224 ± 11.707	12.248 ± 11.686
25	A	83.1346048 ± 0003653	−51.4140969 ± 0003674	2015-02-21	106.814 ± 2.48	137.433 ± 2.484	174.061 ± 2.482
	B	83.1359277 ± 0032688	−51.4139545 ± 0032751	2015-03-25	83.45 ± 23.761	158.756 ± 23.832	179.353 ± 23.817	23.364 ± 23.89	21.323 ± 23.961	31.631 ± 23.922
26	A	189.7530615 ± 0002337	−0.9093664 ± 0002861	2014-03-13	−109.464 ± 1.666	−46.147 ± 2.013	118.794 ± 1.723
	B	189.7546283 ± 0005759	−0.9074848 ± 0006148	2014-03-22	−109.687 ± 5.431	−61.573 ± 5.766	125.787 ± 5.513	0.223 ± 5.681	15.426 ± 6.107	15.428 ± 6.107
27	A	196.3634786 ± 000336	−22.7912345 ± 0003236	2017-07-09	−137.418 ± 2.968	2.063 ± 3.02	137.433 ± 2.968
	B	196.3634238 ± 0004029	−22.7898509 ± 0004017	2017-08-31	−146.575 ± 14.522	−20.231 ± 15.312	147.965 ± 14.537	9.157 ± 14.822	22.294 ± 15.607	24.101 ± 15.496
28	A	200.0728026 ± 000611	−40.2161851 ± 0006481	2014-10-18	−14.727 ± 14.628	−129.167 ± 16.618	130.004 ± 16.594
	B	200.0553734 ± 000314	−40.2084978 ± 000343	2014-05-20	−23.624 ± 2.603	−120.376 ± 2.712	122.672 ± 2.708	8.897 ± 14.858	8.791 ± 16.838	12.508 ± 15.867
29	A	305.9567781 ± 0003761	−48.7430579 ± 0004199	2016-02-24	14.067 ± 2.045	−135.67 ± 2.292	136.397 ± 2.29
	B	305.9533633 ± 0006408	−48.7452881 ± 0006845	2016-06-21	17.981 ± 5.364	−127.904 ± 5.744	129.162 ± 5.737	3.914 ± 5.741	7.766 ± 6.184	8.697 ± 6.097
30	A	332.2196288 ± 0002378	−55.1817348 ± 0002615	2015-10-03	−136.067 ± 1.465	6.288 ± 1.529	136.212 ± 1.465
	B	332.2216314 ± 0004927	−55.1822256 ± 0005096	2015-11-26	−135.249 ± 2.78	9.723 ± 2.781	135.598 ± 2.78	0.818 ± 3.142	3.435 ± 3.174	3.531 ± 3.172
31	A	340.2579184 ± 0002945	−45.007344 ± 00032	2015-03-19	270.602 ± 1.938	−150.33 ± 2.114	309.555 ± 1.981
	B	340.2595948 ± 000365	−45.0089825 ± 0003825	2015-07-23	271.007 ± 1.724	−146.575 ± 1.809	308.106 ± 1.744	0.405 ± 2.594	3.755 ± 2.782	3.777 ± 2.78
32	A	351.7652028 ± 0005126	−52.7910943 ± 0005375	2014-05-10	102.662 ± 3.5	−31.86 ± 3.634	107.492 ± 3.512
	B	351.7421728 ± 0002748	−52.7980402 ± 0002734	2014-02-19	109.78 ± 2.967	−30.027 ± 2.953	113.812 ± 2.966	7.118 ± 4.588	1.833 ± 4.683	7.35 ± 4.594
33	A	353.26044 ± 0003137	−63.7892751 ± 0003392	2015-12-30	43.408 ± 2.348	−161.641 ± 2.417	167.368 ± 2.412
	B	353.2612406 ± 0004994	−63.7885657 ± 0005257	2015-12-23	44.617 ± 3.447	−156.7 ± 3.555	162.928 ± 3.547	1.209 ± 4.171	4.941 ± 4.299	5.087 ± 4.292
34	A	356.1829712 ± 000207	0.5201146 ± 0002457	2015-06-30	−93.08 ± 1.302	−103.922 ± 1.565	139.512 ± 1.454
	B	356.180629 ± 0008729	0.5201466 ± 0009094	2015-09-14	−82.033 ± 5.105	−100.468 ± 5.33	129.704 ± 5.241	11.047 ± 5.268	3.454 ± 5.555	11.574 ± 5.295

Notes.

^a Component, where A is the primary and B the secondary of the system. ^b Proper motion difference in R.A. ^c Proper motion difference in decl. ^d Difference in total proper motion.

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4.1. Spectral Type Estimates

4.2. Spectroscopy

4.3. Distance Estimates

Photometric distances were calculated for the secondaries by employing relevant spectro-photometric distance conversions. We used the spectral type estimates from AstroToolBox and derived the corresponding absolute magnitudes from Table 4 in Kiman et al. (2019) and Table 6 in Best et al. (2018). For each photometric system, we calculated distances using the bands covered by the above relations and retained the minimum and maximum values of the photometric system with the best match. For a given magnitude, we estimated an average distance difference between a given subtype (e.g., L5) and its lower and upper neighbors (L4, L6) of ∼ 20% of the subtypes (L5) photometric distance. These estimations were done by comparing the distances of the lower and upper neighbors of a given subtype at different magnitudes and in different bands. Since we assume a spectral type uncertainty of two subtypes for the secondaries, this can lead to distance discrepancies of up to ∼ 40% of the secondary's photometric distance, depending on the quality of the photometry used for the spectral type estimates. A comparison between the parallactic distance of the primaries and the mean photometric distance of the secondaries is presented in Table 3, which also contains the bands used to calculate the minimum and maximum photometric distances as well as the spectral types employed to derive the absolute magnitudes for those calculations. We have illustrated the distance difference between the primaries and the secondaries in Figure 1. Note that for systems #9 and #15, the parallactic distance of the primary is about twice the photometric distance of the secondary, which we discuss further in Section 5.

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Table 3. Comoving Probabilities and Photometric Distances of the Secondaries

Sys.	Comoving	Comoving	Comoving	Δμα	Δμδ	Sep.	Parallactic	Mean Phot.	Δdist.	Min. Phot.	Max. phot.	Band Min.	Band Max.	SpT
#	Prob. (%)	Prob. (%)	Prob. (%)	(mas yr−1)	(mas yr−1)	(AU)	Dist. (pc)	Dist. (pc)	(pc)	Dist. (pc)	Dist. (pc)	Phot. Dist.	Phot. Dist.	Phot. Dist.
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)	(11)	(12)	(13)	(14)	(15)
1	99.8	100.0	98.5	1.856 ± 10.387	7.559 ± 10.513	1569	107.8 ± 1.8	101.9 ± 8.4	6 ± 8.6	99.5 ± 11	104.3 ± 12.6	zNSC	iNSC	L2
2	99.8	100.0	100.0	8.973 ± 11.718	10.211 ± 11.691	1095	55 ± 0.4	42.4 ± 3.5	12.6 ± 3.5	40.8 ± 4.9	44.1 ± 5	W1CWISE	W2CWISE	T5
3	100.0	100.0	100.0	4.382 ± 1.809	2.355 ± 1.934	782	260.7 ± 57.5	282.5 ± 29.9	21.8 ± 64.8	263.4 ± 36.5	301.7 ± 47.3	yPS1	iPS1	M6
4	100.0	100.0	99.9	7.677 ± 2.034	0.959 ± 2.121	794	145.8 ± 1.2	148.9 ± 25	3.1 ± 25	148.7 ± 34.2	149.2 ± 36.4	RPEDR3	GEDR3	M9
5	99.8	99.9	99.8	2.888 ± 13.911	17.449 ± 12.082	504	86.3 ± 0.2	81.6 ± 12.4	4.7 ± 12.4	80 ± 17.7	83.2 ± 17.3	iDES	zDES	M8
6	99.6	99.8	99.1	9.646 ± 5.189	13.974 ± 4.68	1156	145.9 ± 0.7	147.2 ± 21.1	1.3 ± 21.1	145.1 ± 28.8	149.2 ± 30.9	yPS1	zPS1	M8
7	100.0	98.8	100.0	19.526 ± 16.492	2.815 ± 16.64	1396	118.8 ± 0.9	72.3 ± 14.4	46.4 ± 14.4	71 ± 25.4	73.7 ± 13.5	rDES	iDES	L4
8	100.0	100.0	100.0	0.339 ± 3.879	0.23 ± 4.933	776	184.5 ± 0.8	129.3 ± 19.6	55.2 ± 19.6	125.5 ± 27.8	133.1 ± 27.6	iDES	zDES	M8
9	100.0	59.8	100.0	16.929 ± 12.436	0.006 ± 12.602	8487	232.5 ± 1.1	121.8 ± 30.2	110.6 ± 30.2	119.8 ± 43.1	123.9 ± 42.4	W2CWISE	W1CWISE	L9
10	99.9	100.0	99.9	0.647 ± 8.162	1.645 ± 8.019	1691	75.6 ± 0.1	72.3 ± 17.3	3.2 ± 17.3	60.5 ± 9.2	84.2 ± 33.3	zDES	rDES	L4
11	99.6	99.9	99.1	0.098 ± 28.018	6.786 ± 28.114	637	114.6 ± 9.7	115.6 ± 12	1 ± 15.4	115.4 ± 18.1	115.8 ± 15.7	W2CWISE	W1CWISE	L8
12	99.8	99.9	89.0	4.543 ± 7.573	17.459 ± 7.605	5886	155.9 ± 4.6	153.3 ± 12.1	2.6 ± 12.9	152.6 ± 16.2	153.9 ± 17.9	zNSC	iNSC	L1
13	73.6	87.0	25.7	6.841 ± 2.866	18.764 ± 2.625	549	92 ± 0.4	100.8 ± 14	8.8 ± 14	100 ± 19.3	101.6 ± 20.1	JVHS	KVHS	M8
14	99.9	100.0	100.0	3.915 ± 8.094	3.789 ± 8.298	424	80.8 ± 1.4	67.3 ± 8	13.5 ± 8.2	65.5 ± 10	69 ± 12.6	zDES	iDES	L4
15	100.0	4.5	5.7	5.034 ± 5.552	7.988 ± 5.7	1008	258 ± 3.4	128.4 ± 10.7	129.6 ± 11.3	127.5 ± 15.4	129.3 ± 14.9	iNSC	zNSC	L0
16	100.0	100.0	100.0	3.249 ± 4.112	3.461 ± 3.972	958	165 ± 0.8	154.4 ± 17.8	10.6 ± 17.8	150.8 ± 21.5	157.9 ± 28.4	yPS1	iPS1	M7
17	100.0	100.0	99.7	4.896 ± 4.618	2.65 ± 4.701	741	121.6 ± 0.9	121.8 ± 11.5	0.2 ± 11.5	111.7 ± 14	132 ± 18.2	zSDSS	iSDSS	L0
18	100.0	100.0	100.0	10.172 ± 4.778	6.163 ± 4.64	411	157.2 ± 5.9	191.5 ± 29.4	34.3 ± 29.9	185.2 ± 43.7	197.9 ± 39.2	iPS1	yPS1	M8
19	100.0	100.0	100.0	10.014 ± 7.641	11.628 ± 6.879	1128	134.1 ± 0.6	108.6 ± 13.5	25.4 ± 13.5	106.3 ± 18.2	110.9 ± 20	zPS1	iPS1	M9
20	99.8	99.8	99.9	12.289 ± 11.997	1.476 ± 11.784	2556	106.7 ± 0.3	75.6 ± 19.7	31.2 ± 19.7	59.7 ± 8.1	91.5 ± 38.6	zDES	rDES	L5
21	100.0	100.0	100.0	4.937 ± 7.715	5.019 ± 7.558	933	55 ± 0.1	48.9 ± 8.5	6.1 ± 8.5	47.6 ± 13.4	50.2 ± 10.4	W1UWISE	W2UWISE	T3
22	100.0	100.0	100.0	3.312 ± 4.003	1.777 ± 4.07	571	79.5 ± 0.1	71.6 ± 10.8	8 ± 10.8	64.5 ± 9.3	78.7 ± 19.4	rDES	gDES	L0
23	100.0	100.0	100.0	1.174 ± 2.069	1.007 ± 2.016	1217	156.3 ± 2.9	103.3 ± 12.9	52.9 ± 13.2	92.7 ± 16.7	114 ± 19.7	iNSC	rNSC	M9
24	100.0	100.0	100.0	12.246 ± 11.686	0.224 ± 11.707	707	54.4 ± 0.1	55.7 ± 7.6	1.4 ± 7.6	55 ± 10	56.4 ± 11.4	KVHS	JVHS	T0
25	100.0	100.0	100.0	23.364 ± 23.89	21.323 ± 23.961	508	169.1 ± 10.9	150 ± 17.4	19.1 ± 20.5	145.5 ± 21	154.4 ± 27.7	zNSC	iNSC	L3
26	99.3	100.0	99.9	0.223 ± 5.681	15.426 ± 6.107	377	42.8 ± 0.1	37.6 ± 4.3	5.2 ± 4.3	36.7 ± 6.5	38.5 ± 5.7	iPS1	yPS1	L4
27	99.9	99.9	99.9	9.157 ± 14.822	22.294 ± 15.607	716	143.7 ± 16.4	112.3 ± 13.6	31.4 ± 21.3	111.3 ± 19.6	113.2 ± 18.8	W2CWISE	W1CWISE	L3
28	100.0	100.0	91.6	8.897 ± 14.858	8.791 ± 16.838	3697	66.8 ± 0.1	70.7 ± 5.8	3.9 ± 5.8	68.6 ± 7.2	72.9 ± 9.1	H2MASS	K2MASS	L1
29	100.0	100.0	99.4	3.914 ± 5.741	7.766 ± 6.184	1094	96.1 ± 0.3	96.6 ± 9.8	0.5 ± 9.8	93.9 ± 11.3	99.4 ± 16.1	iDES	rDES	L0
30	100.0	100.0	100.0	0.818 ± 3.142	3.435 ± 3.174	431	95.7 ± 0.6	111 ± 12.5	15.3 ± 12.5	109.6 ± 17.2	112.4 ± 18.1	JVHS	HVHS	M9
31	100.0	100.0	99.9	0.405 ± 2.594	3.755 ± 2.782	418	58.2 ± 2.1	60 ± 5	1.8 ± 5.4	59.8 ± 5.8	60.2 ± 8	JVHS	KVHS	L2
32	100.0	100.0	99.7	7.118 ± 4.588	1.833 ± 4.683	6488	115.8 ± 0.2	112.6 ± 10	3.2 ± 10	95.2 ± 13.1	130 ± 15	rNSC	iNSC	L1
33	100.0	100.0	100.0	1.209 ± 4.171	4.941 ± 4.299	323	113.2 ± 5.5	135.5 ± 16.4	22.3 ± 17.3	134.9 ± 23	136 ± 23.3	W1CWISE	W2CWISE	M9
34	100.0	100.0	98.1	11.047 ± 5.268	3.454 ± 5.555	1031	122.5 ± 2.6	119.3 ± 9.2	3.2 ± 9.5	115.8 ± 11.4	122.8 ± 14.3	JVHS	HVHS	L2

Note. Column descriptions: (1) System number. (2) Comoving probability without a distance constraint on the secondary. (3) Comoving probability with a distance constraint on the secondary. (4) Comoving probability calculated by increasing the secondary's distance by 40% (see Section 4.4). (5) Proper motion difference in R.A. (6) Proper motion difference in decl. (7) Projected physical separation. (8) Parallactic distance of the primary. (9) Mean photometric distance of the secondary. (10) Distance difference between the primary. (parallactic distance) and secondary (mean photometric distance). (11) Minimum photometric distance of the secondary for a given photometric system. (12) Maximum photometric distance of the secondary for a given photometric system. (13) Band from which the minimum photometric distance of the secondary was inferred (CWISE and UWISE stand for CatWISE2020 and unWISE DR1, respectively). (14) Band from which the maximum photometric distance of the secondary was inferred. (15) Spectral type estimate used to derive the absolute magnitude for the photometric distance calculations.

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4.4. Chance Alignment

4.5. Literature Information

4.6. Astrometry

4.7. Mass Ratios and Binding Energies

To compute total masses, mass ratios, and binding energies for each system (Table 5), we estimated component masses using a combination of literature references and relations described below. Table 4 lists masses for the primary stars. For mass estimates of the secondaries we used either the Mamajek (2021) relation for sources with absolute G magnitude < 17, or we extrapolated from the spectral type to dynamical mass values computed in Dupuy & Liu (2017). In Figure 5, we overplotted our systems with the collection of very low-mass systems compiled in Faherty et al. (2020) as well as the collection of binaries from Faherty et al. (2021). We have omitted any system with a comoving probability < 98% (#9, #13, and #15). The majority of our sources lie near the locus of field comoving sources as they have estimated total masses > 0.2 M_⊙. Three systems (#2, #11, and #14) have estimated total masses < 0.2 M_⊙ as they contain low-mass secondaries (T5, L8, L4 respectively) with low-mass host stars ( ∼ M7). These three systems are at the low end of the binding energy distribution for field companion systems but are still well contained within the locus of known sources.

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Table 5. Total Masses, Mass Ratios, and Binding Energies

Sys.	Sys.	Sep. a	M1 b	M2 c	Mtot d	M2/M1 e	Ebin f	SpT2 g
#	Name	(AU)	(M⊙)	(M⊙)	(M⊙)		(×1041 erg)
1	NSC J0004 +0451	1568.531	0.170	0.073	0.243	0.427	1.11	L2
2	NSC J0040 −2942	1095.379	0.097	0.034	0.131	0.354	0.42	T5
3	NSC J0042 −2507	782.216	0.128	0.115	0.243	0.901	2.64	M6
4	NSC J0045 −2855	794.110	0.290	0.079	0.369	0.273	4.04	M9
5	NSC J0107 −2658	504.352	0.467	0.090	0.557	0.192	11.67	M8
6	NSC J0126 −2620	1155.583	0.426	0.090	0.516	0.211	4.65	M8
7	NSC J0148 −0357	1395.736	0.226	0.055	0.281	0.245	1.25	L4
8	NSC J0153 −0015	776.150	0.565	0.090	0.655	0.159	9.18	M8
9	NSC J0200 −1254	8486.735	0.660	0.046	0.706	0.069	0.50	L9
10	NSC J0200 −4707	1691.254	0.440	0.055	0.495	0.126	2.00	L4
11	NSC J0205 +0202	637.127	0.084	0.055	0.139	0.659	1.02	L8
12	NSC J0221 −6338	5886.303	0.131	0.073	0.204	0.554	0.23	L1
13	NSC J0228 −5320	548.533	0.403	0.090	0.493	0.223	9.26	M8
14	NSC J0231 −0311	423.614	0.141	0.055	0.196	0.393	2.56	L4
15	NSC J0244 −0517	1007.524	0.405	0.077	0.482	0.191	4.34	L0
16	NSC J0245 −1237	958.154	0.444	0.097	0.541	0.219	6.30	M7
17	NSC J0254 −0852	741.364	0.224	0.077	0.301	0.345	3.26	L0
18	NSC J0412 −2621	411.436	0.113	0.090	0.203	0.795	3.46	M8
19	NSC J0416 −2152	1127.526	0.315	0.079	0.394	0.251	3.09	M9
20	NSC J0435 −3559	2555.901	0.270	0.055	0.325	0.205	0.81	L5
21	NSC J0457 −2300	933.096	0.218	0.046	0.264	0.210	1.50	T3
22	NSC J0504 −4822	570.648	0.310	0.077	0.387	0.249	5.86	L0
23	NSC J0505 −4750	1216.806	0.139	0.079	0.218	0.569	1.26	M9
24	NSC J0523 −5655	706.547	0.195	0.046	0.241	0.235	1.78	T0
25	NSC J0532 −5124	507.731	0.256	0.073	0.329	0.285	5.16	L3
26	NSC J1239 −0054	377.062	0.222	0.055	0.277	0.250	4.54	L4
27	NSC J1305 −2247	715.907	0.630	0.073	0.703	0.116	9.00	L3
28	NSC J1320 −4012	3697.213	0.499	0.073	0.572	0.145	1.38	L1
29	NSC J2023 −4844	1093.871	0.290	0.077	0.367	0.267	2.86	L0
30	NSC J2208 −5510	430.541	0.206	0.079	0.285	0.384	5.29	M9
31	NSC J2241 −4500	418.277	0.297	0.073	0.370	0.244	7.26	L2
32	NSC J2327 −5247	6487.802	0.493	0.073	0.566	0.147	0.78	L1
33	NSC J2333 −6347	322.740	0.570	0.079	0.649	0.139	19.54	M9
34	NSC J2344 +0031	1030.796	0.161	0.073	0.234	0.451	1.60	L2

Notes.

^a Projected physical separation. ^b Primary mass estimate from either Stassun et al. (2019) or Gentile Fusillo et al. (2021). ^c Secondary mass estimate from either Mamajek (2021) for sources with M_G < 17 mag, or from the SpT to dynamical mass values computed in Dupuy & Liu (2017). ^d Total mass (primary mass + secondary mass). ^e Mass ratio (secondary/primary). ^f Binding energy, calculated by multiplying the physical separation by 1.26 to account for the inclination angle and eccentricity of the binary orbits (Fischer & Marcy 1992). ^g Spectral type used to derive the secondary's mass.

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4.8. Age and Mass Estimates for the White Dwarfs

We performed age and initial and final mass estimates for the three white dwarf primaries (systems #25, #27, and #33) included in our sample. We used wdwarfdate ¹⁵ (Kiman et al. in prep.), which is an open-source code that estimates the ages of white dwarfs in a Bayesian framework. It runs a chain of models to estimate the ages and their uncertainties from an effective temperature and surface gravity. The code determines the age of the progenitor star, the cooling age of the white dwarf, and the total age. The age of the ultracool companion can be inferred directly from the total age of the white dwarf, provided that both formed at the same time. wdwarfdate also estimates the initial mass (that of the progenitor star) and the final mass (that of the white dwarf). The code uses the cooling tracks from (Bédard et al. 2020) to estimate the parameters of the white dwarfs, and MIST stellar evolutionary tracks computed with the Modules for Experiments in Stellar Astrophysics (MESA; Paxton et al. 2011, 2013, 2015; Choi et al. 2016; Dotter 2016). See also Lu et al. (2021) who used the code to estimate the age of main-sequence stars comoving with a white dwarf, to compare with the results of their age dating method.

Since our three white dwarfs are in Gentile Fusillo et al. (2021), we had the required parameters to run the code using Cummings et al. (2018) initial-to-final mass relation. As we do not know the composition of our white dwarfs (we are only working from the photometry), we ran the code using the derived T_eff and log g for DA and DB white dwarfs, provided by Gentile Fusillo. The results are presented in Table 6. The final mass estimates are more or less consistent with those from Gentile Fusillo. Since the white dwarf of system #25 has a very low mass (0.256 ± 0.159 M_⊙), which is outside the range of the initial-to-final mass relation described in Cummings et al. (2018), wdwarfdate cannot estimate the main-sequence age and mass of the progenitor star. However, the code can estimate the mass and cooling age of the white dwarf using Bédard et al. (2020) cooling tracks.

Table 6. Age and Initial and Final Mass Estimates of the White Dwarfs

Sys.	WD	Teff a	log gb	Mass c	MS Age d	WD Age e	Tot. Age f	Init. Mass g	Final Mass h
#	Type	(K)		(M⊙)	(Gyr)	(Gyr)	(Gyr)	(M⊙)	(M⊙)
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
25	DA	4960 ± 422	7.225 ± 0.507	0.256 ± 0.159	⋯	2.34 ${}_{-0.91}^{+2.04}$	⋯	⋯	0.33 ${}_{-0.11}^{+0.21}$
25	DB	5043 ± 337	7.321 ± 0.393	0.283 ± 0.133	⋯	2.04 ${}_{-0.65}^{+1.62}$	⋯	⋯	0.32 ${}_{-0.1}^{+0.16}$
27	DA	5373 ± 786	8.076 ± 0.670	0.63 ± 0.383	1.42 ${}_{-1.01}^{+2.15}$	5.25 ${}_{-2.07}^{+2.27}$	7.41 ${}_{-2.06}^{+1.75}$	1.93 ${}_{-0.53}^{+1.18}$	0.65 ${}_{-0.05}^{+0.12}$
27	DB	5266 ± 720	8.003 ± 0.632	0.571 ± 0.355	1.46 ${}_{-1.0}^{+2.14}$	5.39 ${}_{-2.05}^{+2.22}$	7.57 ${}_{-2.01}^{+1.65}$	1.91 ${}_{-0.51}^{+1.09}$	0.65 ${}_{-0.05}^{+0.1}$
33	DA	5243 ± 318	8.067 ± 0.282	0.623 ± 0.175	1.65 ${}_{-0.98}^{+2.05}$	5.52 ${}_{-1.62}^{+1.84}$	7.79 ${}_{-1.59}^{+1.4}$	1.82 ${}_{-0.42}^{+0.83}$	0.64 ${}_{-0.05}^{+0.07}$
33	DB	5147 ± 285	8.002 ± 0.253	0.57 ± 0.143	1.73 ${}_{-0.94}^{+1.92}$	5.73 ${}_{-1.58}^{+1.7}$	8.05 ${}_{-1.5}^{+1.25}$	1.78 ${}_{-0.38}^{+0.71}$	0.63 ${}_{-0.04}^{+0.06}$

Notes.

^abc Effective temperature, surface gravity, and mass estimates from Gentile Fusillo et al. (2021). ^d Main-sequence age (age of the progenitor star). ^e Cooling age of the white dwarf. ^f Total age (main-sequence age + cooling age). ^g Initial mass (mass of the progenitor star). ^h Final mass (mass of the white dwarf).

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4.9. Finder Charts

Figure 6 compares color composites from unWISE NEO7 with DESI Legacy Imaging Surveys (LS) DR9. The purpose of these images is to show the difference between low-resolution surveys such as WISE (FWHM ∼ 6'' for the short channels; Wright et al. 2010) compared to high-resolution surveys such as DES (FWHM ∼ 1''; Abbott et al. 2018) or VISTA VHS (FWHM ∼ 09; Sutherland et al. 2015) when it comes to identifying binary systems that are less widely separated, in which case WISE would only show one blended source rather than the resolved pair.

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Systems #9 and #19 have high tangential velocities of ∼187 and ∼158 km s⁻¹ respectively, suggesting a possible thick disk or halo membership (Carollo et al. 2010; Dupuy & Liu 2012; Belokurov et al. 2018; Amarante et al. 2020). Further study of these systems is required to determine how old or metal poor these objects really are.

Systems #13, #14, and #31 have a primary with a high Gaia RUWE ¹⁶ of ∼1.9, ∼14, and ∼2.7 respectively. A RUWE significantly greater than 1.0 (e.g., >1.4) could indicate that the source is non-single and thus might be an unresolved binary (Penoyre et al. 2020; Belokurov et al. 2020). Given past work suggesting that widely separated ultracool dwarfs from higher mass companions are likely to be found in hierarchical systems, there is an increased probability of finding more hidden companions. (e.g., Burgasser et al. 2003; Faherty et al. 2010; Law et al. 2010). System #31, which is likely a triple system (M+M+L), has already been analyzed in more detail (Kiwy et al. 2021).

Systems #9, #13, and #15 have comoving probabilities well below 100%, when we use a distance constraint in these calculations, indicating that they are likely chance alignments. Systems #9 and #15 also show the largest discrepancies between the primary's parallactic and the secondary's photometric distance (232.5 ± 1.1 pc versus 121.8 ± 30.2 pc and 258 ± 3.4 pc versus 128.4 ± 10.7 pc, respectively), implying that these systems (provided the photometric distance is reasonably correct) cannot be physically bound. Whereas system #13 has a much smaller distance difference of only 8.8 ± 14 pc between the primary and the secondary as well as a higher comoving probability (87.0%) compared to systems #9 and #15 (59.8% and 4.5%, respectively), but still well below that of the majority of the systems (>99%).

We presented the discovery of 34 new, potential comoving systems found by means of NSC DR2 and demonstrated that the catalog's proper motions are well suited for the discovery of comoving systems including late-type objects such as brown dwarfs in the L and T regimes. We also showed that the catalog can be used to find close late-type comoving companions to white dwarfs, providing valuable benchmark systems for the difficult task of estimating brown dwarf ages.

According to the literature, none of the 34 identified objects were previously known to have a comoving companion. Some of the systems stand out as having high tangential velocities, suggesting that they could be candidates for low metallicity benchmark systems. The newly discovered systems expand the known sample of benchmark systems involving L and T dwarfs and thus contribute to the further characterization of cool substellar objects.

Spectroscopic follow-up on individual interesting systems is warranted, for instance, to find out how low the metallicity of the high tangential velocity systems actually is, or to clarify the potential binarity of the primaries with a high Gaia RUWE value.

This work has made use of data and/or services provided by:

• 1.  
  The Astro Data Lab at NSF's National Optical-Infrared Astronomy Research Laboratory. NOIRLab is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under a cooperative agreement with the National Science Foundation.
• 2.  
  The DESI Legacy Imaging Surveys (https://www.legacysurvey.org/acknowledgment).
• 3.  
  The VISTA Science Archive (VSA) holding the image and catalog data products generated by VIRCAM on the Visible and Infrared Survey Telescope for Astronomy (VISTA).
• 4.  
  The European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
• 5.  
  The European Southern Observatory under ESO program VHS 179.A-2010.
• 6.  
  The SIMBAD database (Wenger et al. 2000), operated at CDS, Strasbourg, France.
• 7.  
  The VizieR catalog access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier). The original description of the VizieR service was published in Ochsenbein et al. (2000).
• 8.  
  The Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR19D0030 with the National Aeronautics and Space Administration.
• 9.  
  The SpeX Prism Spectral Libraries, maintained by Adam Burgasser at http://pono.ucsd.edu/~adam/browndwarfs/spexprism.
• 10.  
  The UltracoolSheet, maintained by Will Best, Trent Dupuy, Michael Liu, Rob Siverd, and Zhoujian Zhang, and developed from compilations by Dupuy & Liu (2012); Dupuy & Kraus (2013); Liu et al. (2016); Best et al. (2018), and Best et al. (2021).
• 11.  
  wdwarfdate, an open-source code that estimates the ages of white dwarfs in a Bayesian framework from effective temperature and surface gravity https://github.com/rkiman/wdwarfdate.
• 12.  
  AstroToolBox, a Java tool set for the identification and classification of astronomical objects with a focus on very low-mass and ultracool dwarfs https://github.com/fkiwy/AstroToolBox.

This research was supported by National Science Foundation grant No.s 2007068, 2009136, and 2009177, and J.F. acknowledges support from the Heising-Simons Foundation.

Below, we provide relevant optical and infrared photometry for all components of the 34 systems (Table 7) as well as an analysis of the photometric quality of our sample (Table 8).