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Geballe T.R.,Gemini Observatory | Oka T.,University of Chicago
Astrophysical Journal Letters | Year: 2010

Until now, the known sources in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high-resolution infrared absorption spectroscopy of interstellar gas occupied a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In order to more fully characterize the gas within the r∼180 pc central molecular zone, it is necessary to find additional such sources that cover a much wider longitudinal range of sightlines. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy within 1.2 in longitude and 0.1 in latitude of Sgr A* using the Spitzer GLIMPSE and the Two Micron All Sky Survey catalogs. Here we present spectra of H+ 3 and CO toward two such objects, one located 140 pc west of Sgr A*, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities and also appears to sample a portion of the expanding molecular ring. The spectra toward Sgr B reveal at least 10 absorption components covering over 200kms-1 and by far the largest equivalent width ever observed in an interstellar H + 3 line; they appear to provide the first near-infrared view into that hotbed of star formation. © 2010. The American Astronomical Society. All rights reserved..

Sheppard S.S.,Carnegie Institution of Washington | Trujillo C.A.,Gemini Observatory
Astrophysical Journal Letters | Year: 2010

We present an ultra-deep survey for Neptune Trojans using the Subaru 8.2 m and Magellan 6.5 m telescopes. The survey reached a 50% detection efficiency in the R band at mR = 25.7 mag and covered 49 deg2 of sky. mR = 25.7 mag corresponds to Neptune Trojans that are about 16 km in radius (assuming an albedo of 0.05). A paucity of smaller Neptune Trojans (radii < 45 km) compared with larger ones was found. The brightest Neptune Trojans appear to follow a steep power-law slope (q = 5 ± 1) similar to the brightest objects in the other known stable reservoirs such as the Kuiper Belt, Jupiter Trojans, and main belt asteroids.We find a roll-over for the Neptune Trojans that occurs around a radius of r = 45 ± 10 km (mR = 23.5 ± 0.3), which is also very similar to the other stable reservoirs. All the observed stable regions in the solar system show evidence for Missing Intermediate-Sized Planetesimals (MISPs). This indicates a primordial and not collisional origin, which suggests that planetesimal formation proceeded directly from small to large objects. The scarcity of intermediate- and smaller-sized Neptune Trojans may limit them as being a strong source for the short period comets. ©2010. The American Astronomical Society. All rights reserved.

Riffel R.A.,Federal University of Santa Maria | Storchi-Bergmann T.,Federal University of Rio Grande do Sul | Winge C.,Gemini Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013

We have mapped the gaseous kinematics and the emission-line flux distributions and ratios from the inner≈680 pc radius of the Seyfert 1 galaxy Mrk 79, using two-dimensional (2D) nearinfrared J-and Kl-band spectra obtained with the Gemini instrument Near-Infrared Integral Field Spectrograph at a spatial resolution of ≈100 pc and velocity resolution of ≈40 km s-1. The molecular hydrogen H2 flux distribution presents two spiral arms extending by ≈700 pc, one to the north and another to the south of the nucleus, with an excitation indicating heating by X-rays from the central source. The low-velocity dispersion (Σ ≈ 50 km s-1) and rotation pattern supports a location of the H2 gas in the disc of the galaxy. Blueshifts observed along the spiral arm in the far side of the galaxy and redshifts in the spiral arm in the near side, suggest that the spiral arms are feeding channels of H2 to the inner 200 pc. From channel maps along the H2 λ2.1218 μm emission-line profile we estimate a mass inflow rate of MH2 ≈ 4 × 10-3M⊙ yr-1, which is one order of magnitude smaller than the mass accretion rate necessary to power the active galactic nucleus (AGN) of Mrk 79. The emission from the ionized gas (traced by Paß and [Fe II]λ 1.2570 μm emission lines) is correlated with the radio jet and with the narrow-band [O III] flux distribution. Its kinematics shows both rotation and outflows to the north and south of the nucleus. The ionized gas mass outflow rate through a cross-section with radius ≈320 pc located at a distance of ≈455 pc from the nucleus is Mout ≈ 3.5M⊙ yr-1, which is much larger than the AGN mass accretion rate, indicating that most of the outflowing gas originates in the interstellar medium surrounding the galaxy nucleus, which is pushed away by a nuclear jet © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Liu M.C.,University of Hawaii at Manoa | Dupuy T.J.,University of Hawaii at Manoa | Leggett S.K.,Gemini Observatory
Astrophysical Journal | Year: 2010

Highly unequal-mass ratio binaries are rare among field brown dwarfs, with the mass ratio distribution of the known census described by q (4.9±0.7). However, such systems enable a unique test of the joint accuracy of evolutionary and atmospheric models, under the constraint of coevality for the individual components (the "isochrone test").We carry out this test using two of themost extreme field substellar binaries currently known, the T1 + T6 ε Ind Bab binary and a newly discovered 0′′.14 T2.0 + T7.5 binary, 2MASS J12095613-1004008AB, identified with Keck laser guide star adaptive optics. The latter is the most extreme tight binary resolved to date (q ̃0.5). Based on the locations of the binary components on the Hertzsprung-Russell (H-R) diagram, current models successfully indicate that these two systems are coeval, with internal age differences of log(age) = -0.8±1.3 (-1.0+1.2-1.3) dex and 0.5 +0.4-0.3 (0.3+0.3-0.4) dex for 2MASS J1209-1004AB and ε Ind Bab, respectively, as inferred from the Lyon (Tucson) models. However, the total mass of ε Ind Bab derived from the H-R diagram (≈80 MJup using the Lyon models) is strongly discrepant with the reported dynamical mass. This problem, which is independent of the assumed age of the ε Ind Bab system, can be explained by a ̃ 50-100 K systematic error in the model atmosphere fitting, indicating slightly warmer temperatures for both components; bringing the mass determinations from the H-R diagram and the visual orbit into consistency leads to an inferred age of ≈ 6 Gyr for ε Ind Bab, older than previously assumed. Overall, the two T dwarf binaries studied here, along with recent results from T dwarfs in age and mass benchmark systems, yield evidence for small (≈100 K) errors in the evolutionary models and/or model atmospheres, but not significantly larger. Future parallax, resolved spectroscopy, and dynamical mass measurements for 2MASS J1209-1004AB will enable a more stringent application of the isochrone test. Finally, the binary nature of this object reduces its utility as the primary T3 near-IR spectral typing standard; we suggest SDSS J1206+2813 as a replacement. © 2010. The American Astronomical Society. All rights reserved.

Chiboucas K.,Gemini Observatory | Jacobs B.A.,University of Hawaii at Manoa | Tully R.B.,University of Hawaii at Manoa | Karachentsev I.D.,Russian Academy of Sciences
Astronomical Journal | Year: 2013

We have followed up on the results of a 65 deg2 CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of , we find a galaxy luminosity function slope of -1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size Re ∼ 100 pc and total magnitude estimates and MI ∼ -9.1. © 2013. The American Astronomical Society. All rights reserved.

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