WISEA J041451.67–585456.7 and WISEA J181006.18–101000.5: The First Extreme T-type Subdwarfs?

Schneider, Adam C.; Burgasser, Adam J.; Gerasimov, Roman; Marocco, F.; Gagné, Jonathan; Goodman, S.; Beaulieu, Paul; Pendrill, William; Rothermich, Austin; Sainio, Arttu; Kuchner, Marc J.; Caselden, Dan; Meisner, Aaron M.; Faherty, Jacqueline K.; Mamajek, Eric E.; Hsu, Chih-Chun; Greco, Jennifer J.; Cushing, Michael C.; Kirkpatrick, J. Davy; Bardalez-Gagliuffi, Daniella; Logsdon, Sarah E.; Allers, Katelyn; Debes, John H.

doi:10.3847/1538-4357/ab9a40

Cited by 35 publications

(64 citation statements)

References 71 publications

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“…As discussed in Meisner et al (2020), the color abnormalities in this object, even before a redder J − ch2 measurement was available, were reminiscent of those of WISE J200520.38 +542433.9 (hereafter, WISE 2005+5424; Mace et al 2013). Shown as an outlying blue square on Figure 3 Other WISE discoveries of unknown distance but occupying a similar locus of color space as WISE 2005+5424 also show spectroscopic indications of low metallicity (Schneider et al 2020;Meisner et al 2021). New atmospheric models, called LOWZ, are presented in Meisner et al (2021) and show that cold brown dwarfs tend to drift bluer in ch1−ch2 and redder in J − ch2 at a fixed temperature as metallicity decreases, which fits the trend expected if WISE 1534−1043 is a more metalpoor subdwarf than WISE 2005+5424.…”

Section: Extremely Low Metallicity (Old) Brown Dwarfmentioning

confidence: 80%

The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. “The Accident”)

Kirkpatrick

Marocco

Caselden

et al. 2021

ApJL

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Continued follow-up of WISEA J153429.75−104303.3, announced in Meisner et al., has proven it to have an unusual set of properties. New imaging data from Keck/MOSFIRE and HST/WFC3 shows that this object is one of the few faint proper motion sources known with J − ch2 >8 mag, indicating a very cold temperature consistent with the latest known Y dwarfs. Despite this, it has W1−W2 and ch1−ch2 colors ∼1.6 mag bluer than a typical Y dwarf. A new trigonometric parallax measurement from a combination of WISE, Spitzer, and HST astrometry confirms a nearby distance of -+ 16.3 1.2 1.4 pc and a large transverse velocity of 207.4 ± 15.9 km s −1 . The absolute J, W2, and ch2 magnitudes are in line with the coldest known Y dwarfs, despite the highly discrepant W1−W2 and ch1−ch2 colors. We explore possible reasons for the unique traits of this object and conclude that it is most likely an old, metal-poor brown dwarf and possibly the first Y subdwarf. Given that the object has an HST F110W magnitude of 24.7 mag, broadband spectroscopy and photometry from JWST are the best options for testing this hypothesis.

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Section: Extremely Low Metallicity (Old) Brown Dwarfmentioning

confidence: 80%

The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. “The Accident”)

Kirkpatrick

Marocco

Caselden

et al. 2021

ApJL

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“…Inasmuch as molecular absorption strengths dictate the overall spectral energy distribution of Y dwarfs (Figure 15 of Doré et al 2016), slight changes in metallicity could affect the relative importance of these bands and dramatically alter Y dwarf spectra and colors. Recent discoveries at early-T from Schneider et al (2020) and A. M. Meisner et al (private communication) underscore the point that warmer brown dwarfs with presumably lower metallicity ([Fe/H] −1 dex) exist; their spectra are vastly different, at least in the near-infrared, from those of solar-metallicity T dwarfs. These may be harbingers of the photometric and spectroscopic bizarreness we can expect from the majority of later Y dwarfs, even if these Y dwarfs in general have less extreme metallicities.…”

Section: The Age Distributionmentioning

confidence: 97%

The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs

Kirkpatrick

Gelino

Faherty

et al. 2021

ApJS

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We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of colormagnitude and color-color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a T eff value and judge sample completeness over bins of T eff and spectral type. Except for types T8 and T eff < 600 K, our census is statistically complete to the 20 pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law ( µ a -dN dM M ) with α = 0.6 ± 0.1. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200 K < T eff < 1350 K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs Y0.5 and with T eff < 400 K. We

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“…We therefore sought to identify esdT candidates based on the combination of W1, W2, and J photometry. esdTs inhabit a distinctive region of J−W2 versus W1−W2 color-color space (see Figure 1, which is based on Figure 3 of Schneider et al 2020). esdTs have much redder J −W2 colors than do T dwarfs in the same 1.1 mag W1 −W2 1.75 mag WISE color range.…”

Section: Selection Of New Extreme T Subdwarf Candidatesmentioning

confidence: 99%

“…Hundreds of T dwarfs (450 K  T eff  1400 K; e.g., Nakajima et al 1995;Kirkpatrick et al 2011;Mace et al 2013a) and dozens of low-metallicity T subdwarfs (e.g., Burningham et al 2014;Pinfield et al 2014;Zhang et al 2019) are now known. Recently, the Backyard Worlds: Planet 9 citizen science project (backyardworlds.org; Kuchner et al 2017, henceforth Backyard Worlds) discovered the first two examples of "extreme T-type subdwarfs" (esdTs; Schneider et al 2020), with T eff  1400 K and [Fe/H] −1. The esdTs have distinctive near-infrared (NIR) colors unlike those of other brown dwarfs and spectra not wellreplicated by any existing models.…”

Section: Introductionmentioning

confidence: 99%

“…Backyard Worlds discoveries have spanned multiple subtopics within solar neighborhood science, including extremely cold Y dwarfs (Bardalez Gagliuffi et al 2020;Meisner et al 2020), co-moving companions (e.g., Faherty et al 2020;Jalowiczor et al 2021;Rothermich et al 2021), T dwarfs (e.g., Kuchner et al 2017), white dwarf disks (Debes et al 2019), and previously overlooked members of the 20 pc brown dwarf census (Kirkpatrick et al 2021). Backyard Worlds revealed the first two known examples of extreme T subdwarfs (Schneider et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project

Meisner

Schneider

Burgasser

et al. 2021

ApJ

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Schneider et al. presented the discovery of WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5, which appear to be the first examples of extreme T-type subdwarfs (esdTs; metallicity −1 dex, T eff  1400 K). Here, we present new discoveries and follow-up of three T-type subdwarf candidates, with an eye toward expanding the sample of such objects with very low metallicity and extraordinarily high kinematics, properties that suggest membership in the Galactic halo. Keck/NIRES near-infrared spectroscopy of WISEA J155349.96 +693355.2, a fast-moving object discovered by the Backyard Worlds: Planet 9 citizen science project, confirms that it is a mid-T subdwarf. With H W2 = 22.3 mag, WISEA J155349.96+693355.2 has the largest W2 reduced proper motion among all spectroscopically confirmed L and T subdwarfs, suggesting that it may be kinematically extreme. Nevertheless, our modeling of the WISEA J155349.96+693355.2 near-infrared spectrum indicates that its metallicity is only mildly subsolar. In analyzing the J155349.96+693355.2 spectrum, we present a new grid of low-temperature, low-metallicity model atmosphere spectra. We also present the discoveries of two new esdT candidates, CWISE J073844.52−664334.6 and CWISE J221706.28−145437.6, based on their large motions and colors similar to those of the two known esdT objects. Finding more esdT examples is a critical step toward mapping out the spectral sequence and observational properties of this newly identified population.

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WISEA J041451.67–585456.7 and WISEA J181006.18–101000.5: The First Extreme T-type Subdwarfs?

Cited by 35 publications

References 71 publications

The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. “The Accident”)

The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. “The Accident”)

The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs

New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project

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