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Recent surveys have revealed that planets intermediate in size between Earth and Neptune ("super-Earths") are among the most common planets in the Galaxy. Atmospheric studies are the next step toward developing a comprehensive understanding of this new class of object. Much effort has been focused on using transmission spectroscopy to characterize the atmosphere of the super-Earth archetype GJ 1214b, but previous observations did not have sufficient precision to distinguish between two interpretations for the atmosphere. The planet's atmosphere could be dominated by relatively heavy molecules, such as water (e.g., a 100% water vapor composition), or it could contain high-altitude clouds that obscure its lower layers. Here we report a measurement of the transmission spectrum of GJ 1214b at near-infrared wavelengths that definitively resolves this ambiguity. These data, obtained with the Hubble Space Telescope, are sufficiently precise to detect absorption features from a high mean molecular mass atmosphere. The observed spectrum, however, is featureless. We rule out cloud-free atmospheric models with water-, methane-, carbon monoxide-, nitrogen-, or carbon dioxide-dominated compositions at greater than 5$\sigma$ confidence. The planet's atmosphere must contain clouds to be consistent with the data., Comment: Accepted for publication in the January 2, 2014 edition of Nature. Includes supplementary information

Our Spitzer IRS observation of the infrared companion Glass Ib revealed fine structure emission with high ionization ([NeIII]/[NeII]=2.1 and [SIV]/[SIII]=0.6) that indicates the gas is likely illuminated by hard radiation. While models suggest extreme ultraviolet radiation could be present in T Tauri stars (Hollenbach & Gorti 2009 and references therein), this is the first detection of [SIV] and such a high [NeIII]/[NeII] ratio in a young star. We also find that Glass Ib displays the molecules HCN, CO2, and H2O in emission. Here we investigate the Glass I binary system and consider possible mechanisms that may have caused the high ionization, whether from an outflow or disk irradiation. We also model the spectral energy distributions of Glass Ia and Ib to test if the system is a young member of the Chameleon I star-forming region, and consider other possible classifications for the system. We find Glass Ib is highly variable, showing changes in continuum strength and emission features at optical, near-infrared, and mid-infrared wavelengths. The optical light curve indicates that a central stellar component in Glass Ib became entirely visible for 2.5 years beginning in mid-2002, and that possibly displayed periodic variability with repeated, short-period dimming during that time. As the fine structure emission was not detected in observations before or after our Spitzer IRS observation, we explore whether the variable nature of Glass Ib is related to the gas being highly ionized, possibly due to variable accretion or an X-ray flare., Comment: 13 pages, 11 figures, Accepted for publication in ApJ

LP 876-10 is a nearby active M4 dwarf in Aquarius at a distance of 7.6 pc. The star is a new addition to the 10-pc census, with a parallax measured via the Research Consortium on Nearby Stars (RECONS) astrometric survey on the Small & Moderate Aperture Research Telescope System's (SMARTS) 0.9-m telescope. We demonstrate that the astrometry, radial velocity, and photometric data for LP 876-10 are consistent with the star being a third, bound, stellar component to the Fomalhaut multiple system, despite the star lying nearly 6 degrees away from Fomalhaut A in the sky. The 3D separation of LP 876-10 from Fomalhaut is only 0.77+-0.01 pc, and 0.987+-0.006 pc from TW PsA (Fomalhaut B), well within the estimated tidal radius of the Fomalhaut system (1.9 pc). LP 876-10 shares the motion of Fomalhaut within ~1 km/s, and we estimate an interloper probability of ~10^{-5}. Neither our echelle spectroscopy nor astrometry are able to confirm the close companion to LP 876-10 reported in the Washington Double Star Catalog (WSI 138). We argue that the Castor Moving Group to which the Fomalhaut system purportedly belongs, is likely to be a dynamical stream, and hence membership to the group does not provide useful age constraints for group members. LP 876-10 (Fomalhaut C) has now risen from obscurity to become a rare example of a field M dwarf with well-constrained age (440+-40 Myr) and metallicity. Besides harboring a debris disk system and candidate planet, Fomalhaut now has two of the widest known stellar companions., Comment: 43 pages, 5 figures, AJ, in press, emulateapj version can be downloaded at: http://www.pas.rochester.edu/~emamajek/fomc/index.html

We present ground-based observations of the nu_1 and nu_3 fundamental bands of H2O toward the massive protostar AFGL 2136 IRS 1, identifying absorption features due to 47 different ro-vibrational transitions between 2.468 micron and 2.561 micron. Analysis of these features indicates the absorption arises in warm (T=506+-25 K), very dense (n(H2)>5*10^9 cm^-3) gas, suggesting an origin close to the central protostar. The total column density of warm water is estimated to be N(H2O)=(1.02+-0.02)*10^19 cm^-2, giving a relative abundance of N(H2O)/N(H2)~10^-4. Our study represents the first extensive use of water vapor absorption lines in the near infrared, and demonstrates the utility of such observations in deriving physical parameters., Comment: 17 pages, 4 figures, 1 table, accepted for publication in The Astrophysical Journal

Since the first report of a potentially non-solar carbon-to-oxygen ratio (C/O) in its dayside atmosphere, the highly irradiated exoplanet WASP-12b has been under intense scrutiny and the subject of many follow-up observations. Additionally, the recent discovery of stellar binary companions ~1" from WASP-12 has obfuscated interpretation of the observational data. Here we present new ground-based multi-object transmission-spectroscopy observations of WASP-12b that we acquired over two consecutive nights in the red optical with Gemini-N/GMOS. After correcting for the influence of WASP-12's stellar companions, we find that these data rule out a cloud-free, H2 atmosphere with no additional opacity sources. We detect features in the transmission spectrum that may be attributed to metal oxides (such as TiO and VO) for an O-rich atmosphere or to metal hydrides (such as TiH) for a C-rich atmosphere. We also reanalyzed NIR transit-spectroscopy observations of WASP-12b from HST/WFC3 and broadband transit photometry from Warm Spitzer. We attribute the broad spectral features in the WFC3 data to either H2O or CH4 and HCN for an O-rich or C-rich atmosphere, respectively. The Spitzer data suggest shallower transit depths than the models predict at infrared wavelengths, albeit at low statistical significance. A multi-instrument, broad-wavelength analysis of WASP-12b suggests that the transmission spectrum is well approximated by a simple Rayleigh scattering model with a planet terminator temperature of 1870 +/- 130 K. We conclude that additional high-precision data and isolated spectroscopic measurements of the companion stars are required to place definitive constraints on the composition of WASP-12b's atmosphere., Comment: 18 pages, 22 figures, accepted for publication in ApJ

We present ground-based measurements of the transmission and emission spectra of the hot-Jupiter WASP-19b in nine spectroscopic channels from 1.25 to 2.35 microns. The measurements are based on the combined analysis of time-series spectroscopy obtained during two complete transits and two complete secondary eclipses of the planet. The observations were performed with the MMIRS instrument on the Magellan II telescope using the technique of multi-object spectroscopy with wide slits. We compare the transmission and emission data to theoretical models to constrain the composition and thermal structure of the planet's atmosphere. Our measured transmission spectrum exhibits a scatter that corresponds to 1.3 scale heights of the planet's atmosphere, which is consistent with the size of spectral features predicted by theoretical models for a clear atmosphere. We detected the secondary eclipses of the planet at significances ranging from 2.2 to 14.4 sigma. The secondary eclipse depths, and the significances of the detections increase towards longer wavelengths. Our measured emission spectrum is consistent with a 2250 K effectively isothermal 1-D model for the planet's dayside atmosphere. This model also matches previously published photometric measurements from the Spitzer Space Telescope and ground-based telescopes. These results demonstrate the important role that ground-based observations using multi-object spectroscopy can play in constraining the properties of exoplanet atmospheres, and they also emphasize the need for high-precision measurements based on observations of multiple transits and eclipses., Comment: ApJ in press

We report the first detection of the v=1--0, R(0) ro-vibrational transition of HF at 2.499385 microns arising from interstellar gas. The line is seen in absorption toward 3 background sources---HD 154368, Elias 29, and AFGL 2136 IRS 1---all of which have reported H2 column densities determined from observations of H2. This allows for the first direct determination of the HF/H2 abundance ratio. We find values of N(HF)/N(H2)=1.15*10^-8 and 0.69*10^-8 for HD 154368 and Elias 29, respectively. The sight line toward AFGL 2136 IRS 1 also shows absorption from the v=1--0, R(1) transition of HF, indicating warm, dense (n_H > 10^9 cm^-3) gas, likely very close to the central protostar. Ascribing portions of the HF absorption to warm and cold gas, we find N(HF)/N(H2)=(1.7--2.9)*10^-8 and (0.33--0.58)*10^-8 for the two components, respectively. Except for the warm component toward AFGL 2136 IRS 1, all observed HF/H2 ratios are well below N(HF)/N(H2)=3.6*10^-8, the value predicted if nearly all gas-phase fluorine is in the form of HF. Models of fluorine chemistry that account for depletion onto grains are able to reproduce the results toward HD 154368, but not in the cold, dense gas toward AFGL 2136 IRS 1 and Elias 29. Most likely, some combination of simplifying assumptions made in the chemical models are responsible for these discrepancies., Comment: 10 pages, 4 figures, 3 tables, accepted to ApJ

We present findings for DoAr 24E, a binary system that includes a classical infrared companion. We observed the DoAr 24E system with the Spitzer Infrared Spectrograph (IRS), with high-resolution, near-infrared spectroscopy of CO vibrational transitions, and with mid-infrared imaging. The source of high extinction toward infrared companions has been an item of continuing interest. Here we investigate the disk structure of DoAr 24E using the column densities, temperature, and velocity profiles of two CO absorption features seen toward DoAr 24Eb. We model the SEDs found using T-ReCS imaging, and investigate the likely sources of extinction toward DoAr 24Eb. We find the lack of silicate absorption and small CO column density toward DoAr 24Eb suggest the mid-infrared continuum is not as extinguished as the near-infrared, possibly due to the mid-infrared originating from an extended region. This, along with the velocity profile of the CO absorption, suggests the source of high extinction is likely due to a disk or disk wind associated with DoAr 24Eb., Comment: 8 pages, 6 figures. Accepted for publication in ApJ

Analyzing exoplanets detected by radial velocity or transit observations, we determine the multiplicity of exoplanet host stars in order to study the influence of a stellar companion on the properties of planet candidates. Matching the host stars of exoplanet candidates detected by radial velocity or transit observations with online multiplicity catalogs in addition to a literature search, 57 exoplanet host stars are identified having a stellar companion. The resulting multiplicity rate of at least 12 percent for exoplanet host stars is about four times smaller than the multiplicity of solar like stars in general. The mass and the number of planets in stellar multiple systems depend on the separation between their host star and its nearest stellar companion, e.g. the planetary mass decreases with an increasing stellar separation. We present an updated overview of exoplanet candidates in stellar multiple systems, including 15 new systems (compared to the latest summary from 2009)., Comment: 11 pages, 4 figures, appendix with 6 tables, accepted for publication in A&A

The star-forming regions in Chamaeleon are one of the nearest (distance ~165 pc) and youngest (age ~2 Myrs) conglomerates of recently formed stars and the ideal target for population studies of star formation. We investigate a total of 16 Cha targets, which have been suggested, but not confirmed as binaries or multiple systems in previous literature. We used the adaptive optics instrument Naos-Conica (NACO) at the Very Large Telescope Unit Telescope 4 of the Paranal Observatory, at 2-5 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and K band. On the basis of known proper motions and these observations, we analyse the astrometric results in our "Proper Motion Diagram" (PMD: angular separation / position angle versus time), to eliminate possible (non-moving) background stars, establish co-moving binaries and multiples, and search for curvature as indications for orbital motion. All previously suggested close components are co-moving and no background stars are found. The angular separations range between 0.07 and 9 arcseconds, corresponding to projected distances between the components of 6-845 AU. Thirteen stars are at least binaries and the remaining three (RX J0919.4-7738, RX J0952.7-7933, VW Cha) are confirmed high-order multiple systems with up to four components. In 13 cases, we found significant slopes in the PMDs, which are compatible with orbital motion whose periods range from 60 to 550 years. However, in only four cases there are indications of a curved orbit, the ultimate proof of a gravitational bond. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components. (abridged), Comment: 33 pages, 22 figures, accepted for publication in A&A, 2nd version: typos and measurement unit added in Table 2

New instrumental capabilities and the wealth of astrophysical information extractable from the near-infrared wavelength region have led to a growing interest in the field of high resolution spectroscopy at 1-5 mu. We aim to provide a library of observed high-resolution and high signal-to-noise-ratio near-infrared spectra of stars of various types throughout the Hertzsprung-Russell diagram. This is needed for the exploration of spectral features in this wavelength range and for comparison of reference targets with observations and models. High quality spectra were obtained using the CRIRES near-infrared spectrograph at ESO's VLT covering the range from 0.97 to 5.3 mu at high spectral resolution. Accurate wavelength calibration and correction for of telluric lines were performed by fitting synthetic transmission spectra for the Earth's atmosphere to each spectrum individually. We describe the observational strategy and the current status and content of the library which includes 13 objects. The first examples of finally reduced spectra are presented. This publication will serve as a reference paper to introduce the library to the community and explore the extensive amount of material., Comment: accepted for publication in A&A; see also the project webpage http://www.univie.ac.at/crirespop

Strong surface magnetic fields are frequently found in the spectra of M-dwarfs, with the mean intensities on the order of a few thousand Gauss - three orders of magnitude higher than the mean surface magnetic field of the Sun. The appearance of such fields in both partially and fully convective M-dwarfs provides strong constraints on the theoretical models of stellar magnetism. The accurate estimates of the magnetic field intensity and geometry in these cool objects, however, is strongly limited to our ability to simulate the Zeeman effect in molecular lines. Here we present the first quantitative results of modelling and analysis of the magnetic fields in selected M-dwarfs in FeH Wing-Ford F\^4Δ-X\^4Δ transitions and some strong atomic lines from polarised radiative transfer.

We present an investigation of the transmission spectrum of the 6.5 M_earth planet GJ1214b based on new ground-based observations of transits of the planet in the optical and near-infrared, and on previously published data. Observations with the VLT+FORS and Magellan+MMIRS using the technique of multi-object spectroscopy with wide slits yielded new measurements of the planet's transmission spectrum from 0.61 to 0.85 micron, and in the J, H, and K atmospheric windows. We also present a new measurement based on narrow-band photometry centered at 2.09 micron with the VLT+HAWKI. We combined these data with results from a re-analysis of previously published FORS data from 0.78 to 1.00 micron using an improved data reduction algorithm, and previously reported values based on Spitzer data at 3.6 and 4.5 micron. All of the data are consistent with a featureless transmission spectrum for the planet. Our K-band data are inconsistent with the detection of spectral features at these wavelengths reported by Croll and collaborators at the level of 4.1 sigma. The planet's atmosphere must either have at least 70% water by mass or optically thick high-altitude clouds or haze to be consistent with the data., Comment: (v2) ApJ in press, no major changes from v1

We present findings for DG Tau B and VV CrA, two of the objects observed in our Spitzer IRS project to search for molecular absorption in edge-on disks, along with near-IR spectroscopy of the CO fundamental transitions and mid-IR imaging. While the only gas absorption seen in the Spitzer IRS spectrum toward DG Tau B is CO$_{2}$, we use gas abundances and gas/ice ratios to argue that we are probing regions of the disk that have low organic molecule abundances. This implies the rarity of detecting molecular absorption toward even edge-on disks with Spitzer IRS is a result of high dependence on the line of sight. We also argue the disk around DG Tau B shows high amounts of grain growth and settling. For VV CrA, we use the silicate absorption feature to estimate a dust extinction, and model the disk with a spectral energy distribution fitting tool to give evidence in support of the disk geometry presented by Smith et al. (2009) where the Primary disk is the main source of extinction toward the infrared companion., Comment: 29 pages, 11 figures, 9 tables. Accepted for publication in Astrophysical Journal

We present an investigation of the transmission spectrum of the 6.5 M ? planet GJ?1214b based on new ground-based observations of transits of the planet in the optical and near-infrared, and on previously published data. Observations with the VLT + FORS and Magellan + MMIRS using the technique of multi-object spectroscopy with wide slits yielded new measurements of the planet's transmission spectrum from 0.61 to 0.85 ?m, and in the J, H, and K atmospheric windows. We also present a new measurement based on narrow-band photometry centered at 2.09 ?m with the VLT + HAWKI. We combined these data with results from a reanalysis of previously published FORS data from 0.78 to 1.00 ?m using an improved data reduction algorithm, and previously reported values based on Spitzer data at 3.6 and 4.5 ?m. All of the data are consistent with a featureless transmission spectrum for the planet. Our K-band data are inconsistent with the detection of spectral features at these wavelengths reported by Croll and collaborators at the level of 4.1?. The planet's atmosphere must either have at least 70% H2O by mass or optically thick high-altitude clouds or haze to be consistent with the data.

Aims. We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford F-4 Delta - X-4 Delta transitions. Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Lande g-factors for FeH lines in different Hund's cases. Magnetic spectra synthesis was performed with the SYNMAST code. Results. We show that the implementation of different Hund's case for FeH states depending on their quantum numbers allows us to achieve a good fit to the majority of lines in a sunspot spectrum in an automatic regime. Strong magnetic fields are confirmed via the modelling of atomic and FeH lines for three M-dwarfs YZ CMi, EV Lac, and AD Leo, but their mean intensities are found to be systematically lower than previously reported. A much weaker field (1.7-2 kG against 2.7 kG) is required to fit FeH lines in the spectra of GJ 1224. Conclusions. Our method allows us to measure average magnetic fields in very low-mass stars from polarized radiative transfer. The obtained results indicate that the fields reported in earlier works were probably overestimated by about 15-30%. Higher quality observations are needed for more definite results.

We conduct a study of K to M type stars to investigate the activity and the rotation limit in the Hyades. We use a sample of 40 stars in this intermediate-age cluster (~625 Myr) to probe stellar rotation in the threshold region where stellar activity becomes prevalent. Here we present projected equatorial velocities (vsin i) and chromospheric activity measurements (H{\alpha}) that indicate the existence of fast rotators in the Hyades at spectral types where also the fraction of stars with H{\alpha} emission shows a rapid increase ("H{\alpha} limit"). The locus of enhanced rotation (and activity) thus seems to be shifted to earlier types in contrast to what is seen as the rotation limit in field stars. The relation between activity and rotation appears to be similar to the one observed in fields stars., Comment: 7 pages, 5 figures. To appear in the CoolStars16 conference proceedings (Seattle, 2010)

METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to provide imaging and spectroscopic capabilities in the 3 - 14 micron region up to a spectral resolution of 100000. One of the novel concepts of METIS is that of a high-resolution integral field spectrograph (IFS) for a diffraction-limited mid-IR instrument. While this concept has many scientific and operational advantages over a long-slit spectrograph, one drawback is that the spectral resolution changes over the field of view. This has an impact on the procedures to correct for telluric absorption lines imprinted on the science spectra. They are a major obstacle in the quest to maximize spectral fidelity, the ability to distinguish a weak spectral feature from the continuum. The classical technique of division by a standard star spectrum, observed in a single IFS spaxel, cannot simply be applied to all spaxels, because the spectral resolution changes from spaxel to spaxel. Here we present and discuss possible techniques of telluric line correction of METIS IFS spectra, including the application of synthetic model spectra of telluric transmission, to maximize spectral fidelity., Comment: 11 pages, 3 figures; Copyright (2010) Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited

We present radial velocity measurements of a sample of L0-L8 dwarfs observed with VLT/UVES and Keck/HIRES. We combine these measurements with distance and proper motion from the literature to determine space motions for 43 of our targets. We identify nine candidate members of young moving groups, which have ages of 50-600 Myr according to their space motion. From the total velocity dispersion of the 43 L dwarfs, we calculate a kinematic age of ~5 Gyr for our sample. This age is significantly higher than the ~3 Gyr age known for late M dwarfs in the solar neighbourhood. We find that the distributions of the U and V velocity components of our sample are clearly non-Gaussian, placing the age estimate inferred from the full space motion vector into question. The W-component exhibits a distribution more consistent with a normal distribution, and from W alone we derive an age of ~3 Gyr, which is the same age found for late-M dwarf samples. Our brightness-limited sample is probably contaminated by a number of outliers that predominantly bias the U and V velocity components. The origin of the outliers remain unclear, but we suggest that these brown dwarfs may have gained their high velocities by means of ejection from multiple systems during their formation., Comment: 8 pages, accepted for publication in A&A

Molecular FeH provides a large number of sharp and isolated absorption lines that can be used to measure radial velocity, rotation, or magnetic field strength with high accuracy. Our aim is to provide an FeH atlas for M-type stars in the spectral region from 986 nm to 1077 nm (Wing-Ford band). To identify these lines in CRIRES spectra of the magnetically inactive, slowly rotating, M5.5 dwarf GJ1002, we calculated model spectra for the selected spectral region with theoretical FeH line data. In general this line list agrees with the observed data, but several individual lines differ significantly in position or in line strength. After identification of as many as possible FeH lines, we correct the line data for position and line strength to provide an accurate atlas of FeH absorption lines for use in high precision spectroscopy of low mass stars. For all lines, we use a Voigt function to obtain their positions and equivalent widths. Identification with theoretical lines is done by hand. For confirmation of the identified lines, we use statistical methods, cross- correlation techniques, and line intensities. Eventually, we were able to identify FeH lines from the (0, 0), (1, 0), (1, 1), (2, 1), (2, 2), (3, 2), and (4, 3) vibrational bands in the observed spectra and correct the positions of the lines if necessary. The deviations between theoretical and observed positions follow a normal distribution approximately around zero. In order to empirically correct the line strength, we determined Teff, instrumental broadening (rotational broadening) and a van der Waals enhancement factor for FeH lines in GJ1002. We also give scaling factors for the Einstein A values to correct the line strengths. With the identified lines, we derived rotational temperatures from line intensities for GJ1002. ... ., Comment: 14 pages, 16 figures, accepted for publication in A&A

In near-infrared NaCo observations of the young brown dwarf 2MASS J0041353-562112, we discovered a companion a little less than a magnitude fainter than the primary. The binary candidate has a separation of 143 mas, the spectral types are M6.5 and M9.0 for the two components. Colors and flux ratios are consistent with the components being located at the same distance minimizing the probability of the secondary being a background object. The brown dwarf is known to show Li absorption constraining the age to less than ~200 Myr, and it was suspected to show ongoing accretion, indicating an age as low as ~10 Myr. We estimate distance and orbital parameters of the binary as a function of age. For an age of 10 Myr, the distance to the system is 50 pc, the orbital period is 126 yr, and the masses of the components are ~30 and ~15 MJup. The binary brown dwarf fills a so far unoccupied region in the parameters mass and age; it is a valuable new benchmark object for brown dwarf atmospheric and evolutionary models., Comment: 4 pages, 2 figures, accepted by A&A

Observational facilities allow now the detection of optical and IR spectra of young M- and L-dwarfs. This enables empirical comparisons with old M- and L- dwarfs, and detailed studies in comparison with synthetic spectra. While classical stellar atmosphere physics seems perfectly appropriate for old M-dwarfs, more physical and chemical processes, cloud formation in particular, needs to be modelled in the substellar regime to allow a detailed spectral interpretation. Not much is known so far about the details of the inset of cloud formation at the spectral transition region between M and L dwarfs. Furthermore there is observational evidence for diversity in the dust properties of objects having the same spectral type. Do we understand these differences? The question is also how young M- and L-dwarfs need to be classified, which stellar parameter do they have and whether degenerations in the stellar parameter space due to the changing atmosphere physics are present, like in the L-T transition region. The Splinter was driven by these questions which we will use to encourage interactions between observation and theory. Given the recent advances, both in observations and spectral modelling, an intensive discussion between observers and theoreticians will create new synergies in our field.

Radial velocities measured from near-infrared spectra are a potentially powerful tool to search for planets around cool stars and sub-stellar objects. However, no technique currently exists that yields near-infrared radial velocity precision comparable to that routinely obtained in the visible. We describe a method for measuring high-precision relative radial velocities of these stars from K-band spectra. The method makes use of a glass cell filled with ammonia gas to calibrate the spectrograph response similar to the "iodine cell" technique that has been used very successfully in the visible. Stellar spectra are obtained through the ammonia cell and modeled as the product of a Doppler-shifted template spectrum of the object and a spectrum of the cell, convolved with a variable instrumental profile model. A complicating factor is that a significant number of telluric absorption lines are present in the spectral regions containing useful stellar and ammonia lines. The telluric lines are modeled simultaneously as well using spectrum synthesis with a time-resolved model of the atmosphere over the observatory. The free parameters in the complete model are the wavelength scale of the spectrum, the instrumental profile, adjustments to the water and methane abundances in the atmospheric model, telluric spectrum Doppler shift, and stellar Doppler shift. Tests of the method based on the analysis of hundreds of spectra obtained for late M dwarfs over six months demonstrate that precisions of ~5 m/s are obtainable over long timescales, and precisions of better than 3 m/s can be obtained over timescales up to a week. The obtained precision is comparable to the predicted photon-limited errors, but primarily limited over long timescales by the imperfect modeling of the telluric lines., Comment: Accepted for publication in ApJ

The detection of planets around very low-mass stars with the radial velocity method is hampered by the fact that these stars are very faint at optical wavelengths where the most high-precision spectrometers operate. We investigate the precision that can be achieved in radial velocity measurements of low mass stars in the near infrared (nIR) Y-, J-, and H-bands, and we compare it to the precision achievable in the optical. For early-M stars, radial velocity measurements in the nIR offer no or only marginal advantage in comparison to optical measurements. Although they emit more flux in the nIR, the richness of spectral features in the optical outweighs the flux difference. We find that nIR measurement can be as precise than optical measurements in stars of spectral type ~M4, and from there the nIR gains in precision towards cooler objects. We studied potential calibration strategies in the nIR finding that a stable spectrograph with a ThAr calibration can offer enough wavelength stability for m/s precision. Furthermore, we simulate the wavelength-dependent influence of activity (cool spots) on radial velocity measurements from optical to nIR wavelengths. Our spot simulations reveal that the radial velocity jitter does not decrease as dramatically towards longer wavelengths as often thought. The jitter strongly depends on the details of the spots, i.e., on spot temperature and the spectral appearance of the spot. Forthcoming nIR spectrographs will allow the search for planets with a particular advantage in mid- and late-M stars. Activity will remain an issue, but simultaneous observations at optical and nIR wavelengths can provide strong constraints on spot properties in active stars., Comment: accepted by ApJ, v2 accepted revision with new precision calculations, abstract abrideg

We report on observations of several transit events of the transiting planet TrES-2 obtained with the Cassegrain-Teleskop-Kamera at the University Observatory Jena. Between March 2007 and November 2008 ten different transits and almost a complete orbital period were observed. Overall, in 40 nights of observation 4291 exposures (in total 71.52 h of observation) of the TrES-2 parent star were taken. With the transit timings for TrES-2 from the 34 events published by the TrES-network, the Transit Light Curve project and the Exoplanet Transit Database plus our own ten transits, we find that the orbital period is P=(2.470614 +/- 0.000001) d, a slight change by ~0.6 s compared to the previously published period. We present new ephemeris for this transiting planet. Furthermore, we found a second dip after the transit which could either be due to a blended variable star or occultation of a second star or even an additional object in the system. Our observations will be useful for future investigations of timing variations caused by additional perturbing planets and/or stellar spots and/or moons., Comment: 10 pages, 13 figures, 5 tables, acceptes for publication in AN

We report on observations of transit events of the transiting planets XO-1b and TrES-1 with a 25 cm telescope of the University Observatory Jena. With the transit timings for XO-1b from all 50 available XO, SuperWASP, Transit Light Curve (TLC)-Project- and Exoplanet Transit Database (ETD)-data, including our own I-band photometry obtained in March 2007, we find that the orbital period is P= (3.941501 +/- 0.000001) d, a slight change by ~3 s compared to the previously published period. We present new ephemeris for this transiting planet. Furthermore, we present new R-band photometry of two transits of TrES-1. With the help of all available transit times from literature this allows us to refine the estimate of the orbital period: P=(3.0300722 +/- 0.0000002) d. Our observations will be useful for future investigations of timing variations caused by additional perturbing planets and/or stellar spots and/or moons., Comment: 7 pages, 7 figures, 5 tables, accepted for publication in AN

We present a new code for the calculation of the 1D structure and synthetic spectra of accretion disks. The code is an extension of the general purpose stellar atmosphere code PHOENIX and is therefore capable of including extensive lists of atomic and molecular lines as well as dust in the calculations. We assume that the average viscosity can be represented by a critical Reynolds number in a geometrically thin disk and solve the structure and radiative transfer equations for a number of disk rings in the vertical direction. The combination of these rings provides the total disk structure and spectrum. Since the warm inner regions of protoplanetary disks show a rich molecular spectrum, they are well suited for a spectral analysis with our models. In this paper we test our code by comparing our models with high-resolution VLT CRIRES spectra of the T Tauri star GQ Lup., Comment: 9 pages, 9 figures, accepted for publication in Astronomy & Astrophysics

We present a combined analysis of previously published high-precision radial velocities and astrometry for the GJ876 planetary system using a self-consistent model that accounts for the planet-planet interactions. Assuming the three planets so far identified in the system are coplanar, we find that including the astrometry in the analysis does not result in a best-fit inclination significantly different than that found by Rivera and collaborators from analyzing the radial velocities alone. In this unique case, the planet-planet interactions are of such significance that the radial velocity data set is more sensitive to the inclination of the system through the dependence of the interactions on the true masses of the two gas giant planets in the system (planets b and c). The astrometry does allow determination of the absolute orbital inclination (i.e. distinguishing between i and 180-i) and longitude of the ascending node for planet b, which allows us to quantify the mutual inclination angle between its orbit and planet c's orbit when combined with the dynamical considerations. We find that the planets have a mutual inclination of 5.0 +3.9 -2.3 degrees. This result constitutes the first determination of the degree of coplanarity in an exoplanetary system around a normal star. That we find the two planets' orbits are nearly coplanar, like the orbits of the Solar System planets, indicates that the planets likely formed in a circumstellar disk, and that their subsequent dynamical evolution into a 2:1 mean motion resonance only led to excitation of a small mutual inclination. This investigation demonstrates how the degree of coplanarity for other exoplanetary systems could also be established using data obtained from existing facilities., Comment: 9 pages, accepted for publication in A&A

We report on observations of transit events of the transiting planets XO-1b and TrES-1 with the AIU Jena telescope in Grossschwabhausen. Based on our IR photometry (in March 2007) and available transit timings (SuperWASP, XO and TLC-project-data) we improved the orbital period of XO-1b (P = 3.941497$\pm$0.000006) and TrES-1 (P = 3.0300737$\pm$0.000006), respectively. The new ephemeris for the both systems are presented., Comment: 4 pages, 2 figures

Observational facilities allow now the detection of optical and IR spectra of young M‐ and L‐dwarfs. This enables empirical comparisons with old M‐ and L‐ dwarfs, and detailed studies in comparison with synthetic spectra. While classical stellar atmosphere physics seems perfectly appropriate for old M‐dwarfs, more physical and chemical processes, cloud formation in particular, needs to be modelled in the substellar regime to allow a detailed spectral interpretation. Not much is known so far about the details of the inset of cloud formation at the spectral transition region between M and L dwarfs. Furthermore there is observational evidence for diversity in the dust properties of objects having the same spectral type. Do we understand these differences? The question is also how young M‐ and L‐dwarfs need to be classified, which stellar parameter do they have and whether degenerations in the stellar parameter space due to the changing atmosphere physics are present, like in the L‐T transition region. The Splinter was driven by these questions which we will use to encourage interactions between observation and theory. Given the recent advances, both in observations and spectral modelling, an intensive discussion between observers and theoreticians will create new synergies in our field.

We present a compilation of the planet candidates currently known from direct imaging. We have gathered available data from the literature and derive the luminosity of all candidates in a homogeneous way using a bolometric correction, the distances and the K band magnitudes of the objects. In a final step we find the masses of the candidates from a comparison of the luminosity or, if not available, an absolute brightness and several well known hot-start evolutionary models., Comment: 4 pages, 1 figure, Proceedings of the 2nd Subaru International Conference on Exoplanets and Disks: Their Formation and Diversity, Keauhou - Hawaii - USA, 9-12 March 2009; 2nd version: Several typos corrected

We combine multifrequency observations from the millimeter to near infrared wavelengths that demonstrate the spatial distributions of H2, CO, and NH3 emission, which are all manifestations of various shocks driven by outflows of deeply embedded sources in NGC6334I. In addition to the well-known northeast-southwest outflow we detect at least one more outflow in the region by combining observations from APEX, ATCA, SMA, Spitzer and VLT/ISAAC. Potential driving sources will be discussed. NGC6334I exhibits several signs of active star formation and will be a major target for future observatories such as Herschel and ALMA., Comment: 6 pages, 6 figures, appeared in the proceedings of the workshop 'The Universe Under The Microscope - Astrophysics At High Angular Resolution', see http://www.iop.org/EJ/toc/1742-6596/131/1

We present first results from a multi-object spectroscopy campaign in IC2602, the Hyades, the Pleiades, and the Coma cluster using VLT/FLAMES. We analysed the data for radial velocity, rotational velocity, and H-alpha activity. Here, we highlight three aspects of this study in the context of rotational braking and the rotation-activity relationship among low mass stars. Finally we discuss the cluster membership of sources in IC2602., Comment: To appear in the proceedings of Cool Stars XV Conference, 4 pages

We present the first results of a large imaging survey to identify wide brown dwarf companions to stars within 10 pc. We have performed a deep (H-band limit ~ 19.0 mag), wide field (up to 16x16 arcmin) astrometric imaging campaign in two epochs around more than 230 nearby stars. Preliminary results show that the wide low-mass companion fraction is far lower than expected, indicating that interactions with the galactic disk may have removed the weakly bound wide companions around old stars., Comment: To appear in proceedings of Cool Stars XV Conference, 3 pages

High precision radial velocity (RV) measurements in the near infrared are on high demand, especially in the context of exoplanet search campaigns shifting their interest to late type stars in order to detect planets with ever lower mass or targeting embedded pre-main-sequence objects. ESO is offering a new spectrograph at the VLT -- CRIRES -- designed for high resolution near-infrared spectroscopy with a comparably broad wavelength coverage and the possibility to use gas-cells to provide a stable RV zero-point. We investigate here the intrinsic short-term RV stability of CRIRES, both with gas-cell calibration data and on-sky measurements using the absorption lines of the Earth's atmosphere imprinted in the source spectrum as a local RV rest frame. Moreover, we also investigate for the first time the intrinsic stability of telluric lines at 4100 nm for features originating in the lower troposphere. Our analysis of nearly 5 hours of consecutive observations of MS Vel, a M2II bright giant centred at two SiO first overtone band-heads at 4100 nm, demonstrates that the intrinsic short-term stability of CRIRES is very high, showing only a slow and fully compensateable drift of up to 60 m/s after 4.5 hours. The radial velocity of the telluric lines is constant down to a level of approx. +/- 10 m/s (or 7/1000 of one pixel). Utilising the same telluriclines as a rest frame for our radial velocity measurements of the science target, we obtain a constant RV with a precision of approx. +/- 20 m/s for MS Vel as expected for a M-giant., Comment: 12 pages, 6 figures, accepted by A&A

Ribas and collaborators have recently proposed that an additional, ~5 M_earth planet orbits the transiting planet host star GJ436. Long-term dynamical interactions between the two planets leading to eccentricity excitation might provide an explanation for the transiting planet's unexpectedly large orbital eccentricity. In this paper we examine whether the existence of such a second planet is supported by the available observational data when the short-term interactions that would result from its presence are accounted for. We find that the model for the system suggested by Ribas and collaborators lead to predictions that are strongly inconsistent with the measured host star radial velocities, transiting planet primary and secondary eclipse times, and transiting planet orbital inclinations. A search for an alternative two planet model that is consistent with the data yields a number of plausible solutions, although no single one stands out as particularly unique by giving a significantly better fit to the data than the nominal single planet model. We conclude from this study that Ribas and collaborator's general hypothesis of an additional short-period planet in the GJ436 system is still plausible, but that there is not sufficient evidence to support their claim of a planet detection., Comment: Accepted for publication in A&A Letters; (v2) fixed typos

We present time series photometry for six partial transits of GJ436b obtained with the Fine Guidance Sensor instrument on the Hubble Space Telescope (HST). Our analysis of these data yields independent estimates of the host star's radius R_star = 0.505 +0.029/-0.020 R_sun, and the planet's orbital period P = 2.643882 +0.000060/-0.000058 d, orbital inclination i = 85.80 +0.21/-0.25 deg, mean central transit time T_c = 2454455.279241 +0.00026/-0.00025 HJD, and radius R_p = 4.90 +0.45/-0.33 R_earth. The radius we determine for the planet is larger than the previous findings from analyses of an infrared light curve obtained with the Spitzer Space Telescope. Although this discrepancy has a 92% formal significance (1.7 sigma), it might be indicative of systematic errors that still influence the analyses of even the highest-precision transit light curves. Comparisons of all the measured radii to theoretical models suggest that GJ436b has a H/He envelope of ~10% by mass. We also find that the transit times for GJ436b are constant to within 10 s over the 11 planetary orbits that the HST data span. However, the ensemble of published values exhibits a long-term drift and our mean transit time is 128 s later than that expected from the Spitzer ephemeris. The sparseness of the currently available data hinders distinguishing between an error in the orbital period or perturbations arising from an additional object in the system as the cause of the apparent trend. Assuming the drift is due to an error in the orbital period we obtain an improved estimate for it of P = 2.643904 +/- 0.000005 d. This value and our measured transit times will serve as important benchmarks in future studies of the GJ436 system. (abridged), Comment: Accepted for publication in A&A

Neuhaeuser & Comeron (1998, 1999) presented direct imaging evidence, as well as first spectra, of several young stellar and sub-stellar M6- to M8-type objects in the Cha I dark cloud. One of these objects is Cha Halpha 2, classified as brown dwarf candidate in several publications and suggested as possible binary in Neuhaeuser et al. (2002). We have searched around Cha Halpha 2 for close and faint companions with adaptive optics imaging. Two epochs of direct imaging data were taken with the Very Large Telescope (VLT) Adaptive Optics instrument NACO in February 2006 and March 2007 in Ks-band. We retrieved an earlier image from 2005 from the European Southern Observatory (ESO) Science Archive Facility, increasing the available time coverage. After confirmation of common proper motion, we deduce physical parameters of the objects by spectroscopy, like temperature and mass. We find Cha Halpha 2 to be a very close binary of ~0.16 arcsec separation, having a flux ratio of ~0.91, thus having almost equal brightness and indistinguishable spectral types within the errors. We show that the two tentative components of Cha Halpha 2 form a common proper motion pair, and that neither component is a non-moving background object. We even find evidence for orbital motion. A combined spectrum of both stars spanning optical and near-infrared parts of the spectral energy distribution yields a temperature of 3000+/-100 K, corresponding to a spectral type of M6+/-1 and a surface gravity of log g= 4.0 +0.75-0.5, both from a comparison with GAIA model atmospheres. We derive masses of ~0.110 Msun (>0.070 Msun) and ~0.124 Msun (>0.077 Msun) for the two components of Cha Halpha 2, i.e., probably low-mass stars, but one component could possibly be a brown dwarf., Comment: 6 pages, 8 figures, accepted for publication in A&A

We present a refined orbital solution for the components A, B, and C of the nearby late-M type multiple system LHS 1070. By combining astrometric datapoints from NACO/VLT, CIAO/SUBARU, and PUEO/CFHT, as well as a radial velocity measurement from the newly commissioned near infrared high-resolution spectrograph CRIRES/VLT, we achieve a very precise orbital solution for the B and C components and a first realistic constraint on the much longer orbit of the A-BC system. Both orbits appear to be co-planar. Masses for the B and C components calculated from the new orbital solution (M_(B+C) = 0.157 +/- 0.009 M_sun) are in excellent agreement with theoretical models, but do not match empirical mass-luminosity tracks. The preliminary orbit of the A-BC system reveals no mass excess for the A component, giving no indication for a previously proposed fourth (D) component in LHS 1070., Comment: published in A&A, 2008, 484, 429; added CFHT acknowledgement

Neuhaeuser et al. (2005) presented direct imaging evidence for a sub-stellar companion to the young T Tauri star GQ Lup. Common proper motion was highly significant, but no orbital motion was detected. Faint luminosity, low gravity, and a late-M/early-L spectral type indicated that the companion is either a planet or a brown dwarf. We have monitored GQ Lup and its companion in order to detect orbital and parallactic motion and variability in its brightness. We also search for closer and fainter companions. We have taken six more images with the VLT Adaptive Optics instrument NACO from May 2005 to Feb 2007, always with the same calibration binary from Hipparcos for both astrometric and photometric calibration. By adding up all the images taken so far, we search for additional companions. The position of GQ Lup A and its companion compared to a nearby non-moving background object varies as expected for parallactic motion by about one pixel (2 \pi with parallax \pi). We could not find evidence for variability of the GQ Lup companion in the K-band (standard deviation being \pm 0.08 mag), which may be due to large error bars. No additional companions are found with deep imaging. There is now exceedingly high significance for common proper motion of GQ Lup A and its companion. In addition, we see for the first time an indication for orbital motion (about 2 to 3 mas/yr decrease in separation, but no significant change in the position angle), consistent with a near edge-on or highly eccentric orbit. We measured the parallax for GQ Lup A to be \pi = 6.4 \pm 1.9 mas (i.e. 156 \pm 50 pc) and for the GQ Lup companion to be 7.2 \pm 2.1 mas (i.e. 139 \pm 45 pc), both consistent with being in the Lupus I cloud and bound to each other., Comment: A&A in press

The Variable Star One-shot Project (VSOP) is aimed at (1) providing the variability type and spectral type of all unstudied variable stars, (2) process, publish, and make the data available as automatically as possible, and (3) generate serendipitous discoveries. This first paper describes the project itself, the acquisition of the data, the dataflow, the spectroscopic analysis and the on-line availability of the fully calibrated and reduced data. We also present the results on the 221 stars observed during the first semester of the project. We used the high-resolution echelle spectrographs HARPS and FEROS in the ESO La Silla Observatory (Chile) to survey known variable stars. Once reduced by the dedicated pipelines, the radial velocities are determined from cross correlation with synthetic template spectra, and the spectral types are determined by an automatic minimum distance matching to synthetic spectra, with traditional manual spectral typing cross-checks. The variability types are determined by manually evaluating the available light curves and the spectroscopy. In the future, a new automatic classifier, currently being developed by members of the VSOP team, based on these spectroscopic data and on the photometric classifier developed for the COROT and Gaia space missions, will be used. We confirm or revise spectral types of 221 variable stars from the GCVS. We identify 26 previously unknown multiple systems, among them several visual binaries with spectroscopic binary individual components. We present new individual results for the multiple systems V349 Vel and BC Gru, for the composite spectrum star V4385 Sgr, for the T-Tauri star V1045 Sco, and for DM Boo which we re-classify as a BY Draconis variable. The complete data release can be accessed via the VSOP web site., Comment: Accepted for publication in A&A

We present new results from our ongoing multiplicity study of exoplanet host stars, carried out with the infrared camera SofI at ESO-NTT. We have identified new low mass companions to the planet host stars HD101930 and HD65216. HD101930AB is a wide binary systems composed of the planet host star HD101930A and its companion HD101930B which is a M0 to M1 dwarf with a mass of about 0.7Msun separated from the primary by ~73arcsec (2200AU projected separation). HD65216 forms a hierarchical triple system, with a projected separation of 253AU (angular separation of about 7arcsec) between the planet host star HD65216A and its close binary companion HD65216BC, whose two components are separated by only ~0.17arcsec (6AU of projected separation). Two VLT-NACO images separated by 3 years confirm that this system is co-moving to the planet host star. The infrared photometry of HD65216B and C is consistent with a M7 to M8 (0.089Msun), and a L2 to L3 dwarf (0.078Msun), respectively, both close to the sub-stellar limit. An infrared spectrum with VLT-ISAAC of the pair HD65216BC, even though not resolved spatially, confirms this late spectral type. Furthermore, we present H- and K-band ISAAC infrared spectra of HD16141B, the recently detected co-moving companion of the planet host star HD16141A. The infrared spectroscopy as well as the apparent infrared photometry of HD16141B are both fully consistent with a M2 to M3 dwarf located at the distance of the planet host star., Comment: MNRAS accepted, 8 pages, 6 figures, and 1 table

We search for stellar and substellar companions of young nearby stars to investigate stellar multiplicity and formation of stellar and substellar companions. We detect common proper-motion companions of stars via multi-epoch imaging. Their companionship is finally confirmed with photometry and spectroscopy. Here we report the discovery of a new co-moving (13 sigma) stellar companion ~17.8 arcsec (350 AU in projected separation) north of the nearby star HD141272 (21 pc). With EMMI/NTT optical spectroscopy we determined the spectral type of the companion to be M3+-0.5V. The derived spectral type as well as the near infrared photometry of the companion are both fully consistent with a 0.26+-0.07 Msol dwarf located at the distance of HD141272 (21 pc). Furthermore the photometry data rules out the pre-main sequence status, since the system is consistent with the ZAMS of the Pleiades., Comment: 6 pages, 6 figures

We show high resolution spectra of the eclipsing brown dwarf binary 2MASSJ05352184-0546085 taken at the two opposite radial velocity maxima. Comparisons of the TiO bands to model and template spectra are fully consistent with the temperatures previously derived for this system. In particular, the reversal of temperatures with mass - in which the higher-mass primary is cooler than its companion - is confirmed. We measure the projected rotation velocities of the compononents; the primary is rotating at least twice as rapidly as the secondary. At the two radial velocity maxima, Halpha emission lines of both components stick out to either sides of the Halpha central wavelength, which is dominated by nebula emission. This enables us to model the individual Halpha lines of the primary and the secondary. We find that the Halpha emission from the primary is at least 7 times stronger than the emission from the secondary. We conclude that the temperature reversal is very likely due to strong magnetic fields inhibiting convection on the primary., Comment: accepted for ApJ Letters

We show individual high resolution spectra of components A, B, and C of the nearby late-M type multiple system LHS 1070. Component A is a mid-M star, B and C are known to have masses at the threshold to brown dwarfs. From our spectra we measure rotation velocities and the mean magnetic field for all three components individually. We find magnetic flux on the order of several kilo-Gauss in all components. The rotation velocities of the two late-M objects B and C are similar (vsini = 16km/s), the earlier A component is spinning only at about half that rate. This suggests weakening of net rotational braking at late-M spectral type, and that the lack of slowly rotating late-M and L dwarfs is real. Furthermore, we found that magnetic flux in the B component is about twice as strong as in component C at similar rotation rate. This indicates that rotational braking is not proportional to magnetic field strength in fully convective objects, and that a different field topology is the reason for the weak braking in low mass objects., Comment: accepted for publication as A&A Letter