Chemical Equilibrium Abundances in Brown Dwarf and Extrasolar Giant Planet Atmospheres

We calculate detailed chemical abundance profiles for a variety of brown dwarf and extrasolar giant planet atmosphere models, focusing in particular on Gliese 229B, and derive the systematics of the changes in the dominant reservoirs of the major elements with altitude and temperature. We assume an Anders and Grevesse (1989) solar composition of 27 chemical elements and track 330 gas--phase species, including the monatomic forms of the elements, as well as about 120 condensates. We address the issue of the formation and composition of clouds in the cool atmospheres of substellar objects and explore the rain out and depletion of refractories. We conclude that the opacity of clouds of low--temperature ($\le$900 K), small--radius condensibles (specific chlorides and sulfides), may be responsible for the steep spectrum of Gliese 229B observed in the near infrared below 1 \mic. Furthermore, we assemble a temperature sequence of chemical transitions in substellar atmospheres that may be used to anchor and define a sequence of spectral types for substellar objects with T$_{eff}$s from $\sim$2200 K to $\sim$100 K.Comment: 57 pages total, LaTeX, 14 figures, 5 tables, also available in uuencoded, gzipped, and tarred form via anonymous ftp at www.astrophysics.arizona.edu (cd to pub/burrows/chem), submitted to Ap.

A New Pleiades Member at the Lithium Substellar Boundary

We present the discovery of an object in the Pleiades open cluster, named Teide 2, with optical and infrared photometry which place it on the cluster sequence slightly below the expected substellar mass limit. We have obtained low- and high-resolution spectra that allow us to determine its spectral type (M6), radial velocity and rotational broadening; and to detect H$_\alpha$ in emission and Li I 670.8 nm in absorption. All the observed properties strongly support the membership of Teide 2 into the Pleiades. This object has an important role in defining the reappearance of lithium below the substellar limit in the Pleiades. The age of the Pleiades very low-mass members based on their luminosities and absence or presence of lithium is constrained to be in the range 100--120 Myr.Comment: 17 pages, 3 figure

A gradient-forming MipZ protein mediating the control of cell division in the magnetotactic bacterium Magnetospirillum gryphiswaldense

Cell division needs to be tightly regulated and closely coordinated with other cellular processes to ensure the generation of fully viable offspring. Here, we investigate division site placement by the cell division regulator MipZ in the alphaproteobacterium Magnetospirillum gryphiswaldense, a species that forms linear chains of magnetosomes to navigate within the geomagnetic field. We show that M. gryphiswaldense contains two MipZ homologs, termed MipZ1 and MipZ2. MipZ2 localizes to the division site, but its absence does not cause any obvious phenotype. MipZ1, by contrast, forms a dynamic bipolar gradient, and its deletion or overproduction cause cell filamentation, suggesting an important role in cell division. The monomeric form of MipZ1 interacts with the chromosome partitioning protein ParB, whereas its ATP-dependent dimeric form shows non-specific DNA-binding activity. Notably, both the dimeric and, to a lesser extent, the monomeric form inhibit FtsZ polymerization in vitro. MipZ1 thus represents a canonical gradient-forming MipZ homolog that critically contributes to the spatiotemporal control of FtsZ ring formation. Collectively, our findings add to the view that the regulatory role of MipZ proteins in cell division is conserved among many alphaproteobacteria. However, their number and biochemical properties may have adapted to the specific needs of the host organism

2MASS J154043.42-510135.7: a new addition to the 5 pc population

The aim of the project is to find the stars nearest to the Sun and to contribute to the completion of the stellar and substellar census of the solar neighbourhood. We identified a new late-M dwarf within 5 pc, looking for high proper motion sources in the 2MASS-WISE cross-match. We collected astrometric and photometric data available from public large-scale surveys. We complemented this information with low-resolution optical and near-infrared spectroscopy with instrumentation on the ESO NTT to confirm the nature of our candidate. We also present a high-quality medium-resolution VLT/X-shooter spectrum covering the 400 to 2500 nm wavelength range. We classify this new neighbour as an M7.0$\pm$0.5 dwarf using spectral templates from the Sloan Digital Sky Survey and spectral indices. Lithium absorption at 670.8 nm is not detected in the X-shooter spectrum, indicating that the M7 dwarf is older than 600 Myr and more massive than 0.06 M$_{\odot}$. We also derive a trigonometric distance of 4.4 pc, in agreement with the spectroscopic distance estimate, making 2MASS\,J154043.42$-$510135.7 the nearest M7 dwarf to the Sun. This trigonometric distance is somewhat closer than the $\sim$6 pc distance reported by the ALLWISE team, who independently identified this object recently. This discovery represents an increase of 25\% in the number of M7--M8 dwarfs already known at distances closer than 8\,pc from our Sun. We derive a density of $\rho$\,=\,1.9$\pm$0.9$\times$10$^{-3}$\,pc$^{-3}$ for M7 dwarfs in the 8 pc volume, a value similar to those quoted in the literature. This new ultracool dwarf is among the 50 nearest systems to the Sun, demonstrating that our current knowledge of the stellar census within the 5 pc sample remains incomplete. 2M1540 represents a unique opportunity to search for extrasolar planets around ultracool dwarfs due to its proximity and brightness.Comment: 8 pages, 5 figures. Acepted in Astronomy & Astrophysics (15/05/2005

Testing the existence of optical linear polarization in young brown dwarfs

Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases withthe degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using spectroscopy. Linear polarimetric images were collected in I and R-band using CAFOS at the 2.2 m telescope in Calar Alto Observatory (Spain). The flux ratio method was employed to determine the linear polarization degrees. With a confidence of 3$\sigma$, our data indicate that all targets have a linear polarimetry degree in average below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were observed. We detected significant (i.e. P/$\sigma$ $\le$ 3) linear polarization for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of $\mathrm{p^{*}}$ = 0.81 $\pm$ 0.17 %.Comment: Accepted for publication in MNRA

On the nature of the deeply embedded protostar OMC-2 FIR 4

We use mid-infrared to submillimeter data from the Spitzer, Herschel, and APEX telescopes to study the bright sub-mm source OMC-2 FIR 4. We find a point source at 8, 24, and 70 $\mu$m, and a compact, but extended source at 160, 350, and 870 $\mu$m. The peak of the emission from 8 to 70 $\mu$m, attributed to the protostar associated with FIR 4, is displaced relative to the peak of the extended emission; the latter represents the large molecular core the protostar is embedded within. We determine that the protostar has a bolometric luminosity of 37 Lsun, although including more extended emission surrounding the point source raises this value to 86 Lsun. Radiative transfer models of the protostellar system fit the observed SED well and yield a total luminosity of most likely less than 100 Lsun. Our models suggest that the bolometric luminosity of the protostar could be just 12-14 Lsun, while the luminosity of the colder (~ 20 K) extended core could be around 100 Lsun, with a mass of about 27 Msun. Our derived luminosities for the protostar OMC-2 FIR 4 are in direct contradiction with previous claims of a total luminosity of 1000 Lsun (Crimier et al 2009). Furthermore, we find evidence from far-infrared molecular spectra (Kama et al. 2013, Manoj et al. 2013) and 3.6 cm emission (Reipurth et al 1999) that FIR 4 drives an outflow. The final stellar mass the protostar will ultimately achieve is uncertain due to its association with the large reservoir of mass found in the cold core.Comment: Accpeted by ApJ, 17 pages, 11 figure

Scalar Field Dark Matter: behavior around black holes

We present the numerical evolution of a massive test scalar fields around a Schwarzschild space-time. We proceed by using hyperboloidal slices that approach future null infinity, which is the boundary of scalar fields, and also demand the slices to penetrate the event horizon of the black hole. This approach allows the scalar field to be accreted by the black hole and to escape toward future null infinity. We track the evolution of the energy density of the scalar field, which determines the rate at which the scalar field is being diluted. We find polynomial decay of the energy density of the scalar field, and use it to estimate the rate of dilution of the field in time. Our findings imply that the energy density of the scalar field decreases even five orders of magnitude in time scales smaller than a year. This implies that if a supermassive black hole is the Schwarzschild solution, then scalar field dark matter would be diluted extremely fastComment: 15 pages, 21 eps figures. Appendix added, accepted for publication in JCA

Andean Pastures in the Fourth Region of Chile: Marginal Lands and Vital Spaces for a Transhumance System

In the fourth region of Chile, the high Andean pastures between Chile and Argentina are the summer destination for transhumant shepherds and sustain a part of the regional livestock. Since 2000, Chile has prohibited the passage of livestock to Argentina for animal health reasons in spite of official registers indicating that 60 to 75% of the summer transhumance livestock had an Argentine destination. Under those conditions it is questionable whether the Andean Chilean grasslands can absorb the increased pastoral demand without suffering damage. The objective is to provide elements of an answer to this question regarding the distribution and availability of the Andean forage resource and its modalities of explotation in the local transhumance system