High Resolution Spectroscopy during Eclipse of the Young Substellar Eclipsing Binary 2MASS 0535-0546. I. Primary Spectrum: Cool Spots versus Opacity Uncertainties

We present high-resolution Keck optical spectra of the very young substellar eclipsing binary 2MASS J05352184-0546085, obtained during eclipse of the lower-mass (secondary) brown dwarf. The observations yield the spectrum of the higher-mass (primary) brown dwarf alone, with negligible (~1.6%) contamination by the secondary. We perform a simultaneous fine-analysis of the TiO-epsilon band and the red lobe of the KI doublet, using state-of-the-art PHOENIX Dusty and Cond synthetic spectra. Comparing the effective temperature and surface gravity derived from these fits to the {\it empirically} determined surface gravity of the primary (logg=3.5) then allows us to test the model spectra as well as probe the prevailing photospheric conditions. We find that: (1) fits to TiO-epsilon alone imply Teff=2500 \pm 50K; (2) at this Teff, fits to KI imply logg=3.0, 0.5 dex lower than the true value; and (3) at the true logg, KI fits yield Teff=2650 \pm 50K, ~150K higher than from TiO-epsilon alone. On the one hand, these are the trends expected in the presence of cool spots covering a large fraction of the primary's surface (as theorized previously to explain the observed Teff reversal between the primary and secondary). Specifically, our results can be reproduced by an unspotted stellar photosphere with Teff=2700K and (empirical) logg=3.5, coupled with axisymmetric cool spots that are 15% cooler (2300K), have an effective logg=3.0 (0.5 dex lower than photospheric), and cover 70% of the surface. On the other hand, the trends in our analysis can also be reproduced by model opacity errors: there are lacks in the synthetic TiO-epsilon opacities, at least for higher-gravity field dwarfs. Stringently discriminating between the two possibilities requires combining the present results with an equivalent analysis of the secondary (predicted to be relatively unspotted compared to the primary).Comment: To appear in ApJ. 11 pages, 5 figure

A Hot Gap Around Jupiter's Orbit in the Solar Nebula

The Sun was an order of magnitude more luminous during the first few hundred thousand years of its existence, due in part to the gravitational energy released by material accreting from the Solar nebula. If Jupiter was already near its present mass, the planet's tides opened an optically-thin gap in the nebula. We show using Monte Carlo radiative transfer calculations that sunlight absorbed by the nebula and re-radiated into the gap raised temperatures well above the sublimation threshold for water ice, with potentially drastic consequences for the icy bodies in Jupiter's feeding zone. Bodies up to a meter in size were vaporized within a single orbit if the planet was near its present location during this early epoch. Dust particles lost their ice mantles, and planetesimals were partially to fully devolatilized, depending on their size. Scenarios in which Jupiter formed promptly, such as those involving a gravitational instability of the massive early nebula, must cope with the high temperatures. Enriching Jupiter in the noble gases through delivery trapped in clathrate hydrates will be more difficult, but might be achieved by either forming the planet much further from the star, or capturing planetesimals at later epochs. The hot gap resulting from an early origin for Jupiter also would affect the surface compositions of any primordial Trojan asteroids.Comment: 25 pages, 10 figures. ApJ in press. Discussion of Jupiter's volatile enrichment revised in sec. 4.

The onset of X-ray emission in young stellar objects: a Chandra observation of the Serpens star-forming region

AIMS: To study the properties of X-ray emissions from young stellar objects (YSOs), through their evolution from Class I to Class III and determine whether Class 0 protostars emit in X-rays. METHODS: A deep Chandra X-ray observation of the Serpens star-forming region was obtained. The Serpens Cloud Core is ideally suited for this type of investigation, being populated by a dense and extremely young cluster whose members are found in all different evolutionary stages, including six well studied Class 0 sources. RESULTS: None of the six Class 0 protostars is detected in our observations, excluding the presence of sources with X-ray luminosities > 0.4 10^30 erg/s (for column densities of the order of 4 10^{23} cm^-2, or A_V ~ 200). A total of 85 X-ray sources are detected and the light curves and spectra of 35 YSOs are derived. There is a clear trend of decreasing absorbing column densities as one moves from Class I to Class III sources, and, possibly, evidence of decreasing plasma temperatures, too. We observe a strong, long-duration, flare from a Class II low-mass star, for which we derive a flaring loop length of the order of 20 stellar radii. We interpret the flaring event as originating from a magnetic flux tube connecting the star to its circumstellar disk. The presence of such a disk is supported by the detection, in the spectrum of this star, of 6.4 keV Fe fluorescent emission.Comment: Accepted for publication in A&

A survey for Fe 6.4 keV emission in young stellar objects in rho Oph: the strong fluorescence from Elias 29

We report the results of a search for 6.4 keV Fe fluorescent emission in Young Stellar Objects (YSOs) with measured accretion luminosities in the rho Oph cloud, using all existing chandra and XMM-Newton observations of the region. A total of nine such YSOs have X-ray data with sufficiently high S/N for the 6.4 keV line to be potentially detected if present. A positive detection of the Fe 6.4 keV line is reported for one object, Elias 29, in both the XMM-Newton and the chandra data. The 6.4 keV line is detected in Elias 29 both during quiescent and flaring emission, unlikely all previously reported detections of 6.4 keV Fe fluorescence in YSOs which were made during intense flaring. The observed equivalent width of the fluorescent line is large, at W_alpha approx 140 eV, ruling out fluorescence from diffuse circumstellar material. It is also larger than expected for simple reflection from a solar-composition photosphere or circumstellar disk, but it is compatible with being due to fluorescence from a centrally illuminated circumstellar disk. The X-ray spectrum of Elias 29 is also peculiar in terms of its high (ionized) Fe abundance, as evident from the very intense Fe xxv 6.7 keV line emission; we speculate on the possible mechanism leading to the observed high abundance.Comment: Accepted by A&

High resolution spectroscopy of Ne II emission from young stellar objects

Constraining the spatial and thermal structure of the gaseous component of circumstellar disks is crucial to understand star and planet formation. Models predict that the [Ne II] line at 12.81 {\mu}m detected in young stellar objects with Spitzer traces disk gas and its response to high energy radiation, but such [Ne II] emission may also originate in shocks within powerful outflows. To distinguish between these potential origins for mid-infrared [Ne II] emission and to constrain disk models, we observed 32 young stellar objects using the high resolution (R~30000) mid-infrared spectrograph VISIR at the VLT. We detected the 12.81 {\mu}m [Ne II] line in 12 objects, tripling the number of detections of this line in young stellar objects with high spatial and spectral resolution spectrographs. We obtain the following main results: a) In Class I objects the [Ne II] emission observed from Spitzer is mainly due to gas at a distance of more than 20-40 AU from the star, where neon is, most likely, ionized by shocks due to protostellar outflows. b) In transition and pre-transition disks, most of the emission is confined to the inner disk, within 20-40 AU from the central star. c) Detailed analysis of line profiles indicates that, in transition and pre-transition disks, the line is slightly blue-shifted (2-12 km s{^-1}) with respect to the stellar velocity, and the line width is directly correlated with the disk inclination, as expected if the emission is due to a disk wind. d) Models of EUV/X-ray irradiated disks reproduce well the observed relation between the line width and the disk inclination, but underestimate the blue-shift of the line.Comment: 35 pages, 7 figures, accepted for publication on Ap

Preliminary Orbit of the Young Binary Haro 1-14c

Using the Keck Interferometer, we spatially resolved the orbit of the pre-main sequence binary, Haro 1-14c, for the first time. We present these interferometric observations along with additional spectroscopic radial velocity measurements of the components. We performed a simultaneous orbit fit to the interferometric visibilities and the radial velocities of Haro 1-14c. Based on a statistical analysis of the possible orbital solutions that fit the data, we determined component masses of M_1 = 0.96 (+0.27/-0.08) Msun and M_2 = 0.33 (+0.09/-0.02) Msun for the primary and secondary, respectively, and a distance to the system of 111 (+19/-18) pc. The distance measurement is consistent with the close distance estimates of the Ophiuchus molecular cloud. Comparing our results with evolutionary tracks suggests an age of 3-4 Myr for Haro 1-14c. With additional interferometric measurements to improve the uncertainties in the masses and distance, we expect the low-mass secondary to provide important empirical data for calibrating the theoretical evolutionary tracks for pre-main sequence stars.Comment: 28 pages, 9 figures, accepted for publication in A

Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy

An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope