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The New Cool Subdwarfs

The New Cool Subdwarfs. Metal-poor Stars and Brown Dwarfs Extending into the L and T Dwarf Regimes. Adam Burgasser (UCLA) J. Davy Kirkpatrick (Caltech) S é bastien L é pine (AMNH). Kuiper (1939). The Coolest Subdwarfs ca. Cool Stars 12.

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The New Cool Subdwarfs

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  1. The New Cool Subdwarfs Metal-poor Stars and Brown Dwarfs Extending into the L and T Dwarf Regimes Adam Burgasser (UCLA) J. Davy Kirkpatrick (Caltech) Sébastien Lépine (AMNH)

  2. Kuiper (1939)

  3. The Coolest Subdwarfsca. Cool Stars 12 All exhibit late-type M dwarf features (strong TiO, VO). Enhanced metal hydrides (CaH, MgH, FeH) and alkali lines (K I, Na I). Blue NIR colors relative to equivalent disk counterparts. Halo kinematics  generally identified in photographicproper motion surveys (Luyten, APMPM). Gizis (1997)

  4. Cooler Field Dwarf SEDs Peak at Longer Wavelengths Dahn et al. (2002) I-J vs SpT All-sky/wide-area surveys sensitive at NIR wavelengths (2MASS, DENIS, SDSS) have identified >400 L and T dwarfs

  5. Red-Sensitive PM Surveys: Many New Discoveries Lépine, Shara, & Rich (2003,2004) LSR 1425+7102 sdM8 LSR 0822+1700 esdM6.5 See poster by Zinnecker et al.

  6. An Early-type L Subdwarf LSR 1610-0040 Lépine, Shara, & Rich (2003) Many spectral features reminiscent of L field dwarfs (e.g., red optical slope, alkali lines) Optical classification schemes for sdMs do not apply for sdLs

  7. Serendipity in 2MASS • During a search for T dwarfs in the 2MASS survey, we identified the high proper motion object 2MASS 0532+8246. • μ = 2.6 "/yr, Vtan = 320 km/s, Vrad = -195 km/s  halo star • IC-J  4, J-K  0.3 • undetected in DSS photographic plates 10" 2MASS 0532+8246 Δt = 3.2 yr

  8. An L Subdwarf Burgasser et al. (2003) Substantial H- and K-band suppression – CIA H2

  9. An L Subdwarf TiH Burgasser et al. (2003) Very strong metal hydrides; enhanced TiO?

  10. 2MASS 0532+82 is Substellar • Decreased atmospheric metallicity… •  decreased atmospheric opacity •  higher luminosity •  more rapid evolution • Consequences: • Minimum H-burning mass is larger (~0.09 M for Z=0) • After 10 Gyr, few “warm” brown dwarfs left. Burgasser et al. (2003)

  11. New Cool Subdwarfs in 2MASS Six additional ultracool (>sdM7) subdwarfs have now been identified in the same sample. new sdM7.5-sdM8 new early sdL? Burgasser et al. (2004)

  12. T Subdwarfs? • A number of late-type T dwarfs are seen to exhibit subdwarf-like spectral features: • Extremely blue NIR colors (J-K < -0.5) • Broadened 1 μm peaks (Burrows et al. 2002) μ = 2.98 “/yr  Vtan  120 km/s Burgasser et al. (in prep)

  13. Identifying More Ultracool Subdwarfs: NIR PM Surveys CPAPIR 2MASS 0.3" astrometry ca. 1997-2001 See posters by Leggett et al., Nakajima et al.

  14. For Further Reference • Ultracool Subdwarf Discoveries • Burgasser et al. 2003, ApJ, 592, 1186 • Burgasser et al. 2004, AJ, 127, 2896 • Lépine, Rich, & Shara 2003, ApJ, 585, L69 • Lépine, Rich, & Shara 2003, ApJ, 591, L49 • Lépine, Rich, & Shara 2004, ApJ, 602, L125 • Scholz et al. 2004, A&A, in press (astro-ph/0406457) • Metallicity Effects: Atmospheric & Evolutionary Models • Burrows et al. 2001, Rev. Mod. Phys., 73, 719 • Burrows et al. 2002, ApJ, 574, 394 • Hauschildt, Allard, & Baron 1999, ApJ, 512, 377 • Subdwarf Spectra • Gizis 1997, AJ, 113, 806 • Leggett et al. 2000, ApJ, 535, 965

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