Optical spectroscopy of EX Lupi during quiescence and outburst: Infall, wind, and dynamics in the accretion flow

We explore the accretion mechanisms in EX Lupi, prototype of EXor variables, during its quiescence and outburst phases. We analyse high-resolution optical spectra taken before, during, and after its 2008 outburst. In quiescence and outburst, the star presents many permitted emission lines, including typical CTTS lines and numerous neutral and ionized metallic lines. During the outburst, the number of emission lines increases to over a thousand, with narrow plus broad component structure (NC+BC). The BC profile is highly variable on short timescales (24-72h). An active chromosphere can explain the metallic lines in quiescence and the outburst NC. The dynamics of the BC line profiles suggest an origin in a hot, dense, non-axisymmetric, and non-uniform accretion column that suffers velocity variations along the line-of-sight on timescales of days. Assuming Keplerian rotation, the emitting region would be located at ~0.1-0.2 AU, consistent with the inner disk rim, but the velocity profiles of the lines reveal a combination of rotation and infall. Line ratios of ions and neutrals can be reproduced with a temperature of T~6500 K for electron densities of a few times 10$^{12}$cm$^{-3}$ in the line-emitting region. The data confirm that the 2008 outburst was an episode of increased accretion, albeit much stronger than previous EX Lupi and typical EXors outbursts. The line profiles are consistent with the infall/rotation of a non-axisymmetric structure that could be produced by clumpy accretion during the outburst phase. A strong inner disk wind appears in the epochs of higher accretion. The rapid recovery of the system after the outburst and the similarity between the pre-outburst and post-outburst states suggest that the accretion channels are similar during the whole period, and only the accretion rate varies, providing a superb environment for studying the accretion processes.Comment: 15 pages plus 26 pages online material, accepted by A&

Efficient creation of molecules from a cesium Bose-Einstein condensate

We report a new scheme to create weakly bound Cs$_2$ molecules from an atomic Bose-Einstein condensate. The method is based on switching the magnetic field to a narrow Feshbach resonance and yields a high atom-molecule conversion efficiency of more than 30%, a factor of three higher than obtained with conventional magnetic-field ramps. The Cs$_2$ molecules are created in a single $g$-wave rotational quantum state. The observed dependence of the conversion efficiency on the magnetic field and atom density shows scattering processes beyond two-body coupling to occur in the vicinity of the Feshbach resonance.Comment: 7 pages, 4 figures, submitted to Europhysics Letter

Star Formation in the Gulf of Mexico

We present an optical/infrared study of the dense molecular cloud, L935, dubbed "The Gulf of Mexico", which separates the North America and the Pelican nebulae, and we demonstrate that this area is a very active star forming region. A wide-field imaging study with interference filters has revealed 35 new Herbig-Haro objects in the Gulf of Mexico. A grism survey has identified 41 Halpha emission-line stars, 30 of them new. A small cluster of partly embedded pre-main sequence stars is located around the known LkHalpha 185-189 group of stars, which includes the recently erupting FUor HBC 722.Comment: Submitted to A&A, 14 pages, 18 figure

Observation of Feshbach-like resonances in collisions between ultracold molecules

We observe magnetically tuned collision resonances for ultracold Cs2 molecules stored in a CO2-laser trap. By magnetically levitating the molecules against gravity, we precisely measure their magnetic moment. We find an avoided level crossing which allows us to transfer the molecules into another state. In the new state, two Feshbach-like collision resonances show up as strong inelastic loss features. We interpret these resonances as being induced by Cs4 bound states near the molecular scattering continuum. The tunability of the interactions between molecules opens up novel applications such as controlled chemical reactions and synthesis of ultracold complex molecules

IRAS 05436-0007 and the Emergence of McNeil's Nebula

We present a study of McNeil's Nebula, a newly appeared reflection nebula in the L1630 cloud, together with photometry and spectroscopy of its source. New IR photometry compared to earlier 2MASS data shows that the star has brightened by about 3 magnitudes in the near-infrared, changing its location in a J-H/H-K diagram precisely along a reddening vector. A Gemini NIRI K-band spectrum shows strong CO-bandhead emission and Br-gamma is in emission, indicative of strong accretion. A Gemini GMOS optical spectrum shows only a red, heavily veiled continuum, with H-alpha strongly in emission and displaying a pronounced P Cygni profile, with an absorption trough reaching velocities up to 600 km s-1. This implies significant mass loss in a powerful wind. However, no evidence is found for any shocks, as commonly seen in collimated outflows from young stars. Apparently the eruption has dispersed a layer of extinction and this, together with the intrinsic brightening of the IRAS source, has allowed an earlier outflow cavity to be flooded with light, thus creating McNeil's Nebula.Comment: 9 pages, 5 figure

Mapping the CMB I: the first flight of the QMAP experiment

We report on the first flight of the balloon-borne QMAP experiment. The experiment is designed to make a map of the cosmic microwave background anisotropy on angular scales from 0.7 to several degrees. Using the map we determine the angular power spectrum of the anisotropy in multipole bands from l~40 to l~140. The results are consistent with the Saskatoon (SK) measurements. The frequency spectral index (measured at low l) is consistent with that of CMB and inconsistent with either Galactic synchrotron or free-free emission. The instrument, measurement, analysis of the angular power spectrum, and possible systematic errors are discussed.Comment: 4 pages, with 5 figures included. Submitted to ApJL. Window functions and color figures are available at http://pupgg.princeton.edu/~cmb/welcome.htm

`St\"uckelberg interferometry' with ultracold molecules

We report on the realization of a time-domain `St\"uckelberg interferometer', which is based on the internal state structure of ultracold Feshbach molecules. Two subsequent passages through a weak avoided crossing between two different orbital angular momentum states in combination with a variable hold time lead to high-contrast population oscillations. This allows for a precise determination of the energy difference between the two molecular states. We demonstrate a high degree of control over the interferometer dynamics. The interferometric scheme provides new possibilities for precision measurements with ultracold molecules.Comment: 4 pages, 5 figure

V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months

We report on photometric (BVRIJHK) and low dispersion spectroscopic observations of V1647 Ori, the star that drives McNeil's Nebula, between 10 February and 7 May 2004. The star is photometrically variable atop a general decline in brightness of about 0.3-0.4 magnitudes during these 87 days. The spectra are featureless, aside from H-alpha and the Ca II infrared triplet in emission, and a Na I D absorption feature. The Ca II triplet line ratios are typical of young stellar objects. The H-alpha equivalent width may be modulated on a period of about 60 days. The post-outburst extinction appears to be less than 7 mag. The data are suggestive of an FU Orionis-like event, but further monitoring will be needed to definitively characterize the outburst.Comment: Accepted for publication in the Astronomical Journa

Fundamental Vibrational Transition of CO During the Outburst of EX Lupi in 2008

We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental band at 4.6–5.0 μm. The observations were carried out at the Very Large Telescope and the Subaru Telescope at six epochs from 2008 April to August, covering the plateau of the outburst and the fading phase to a quiescent state. The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 μm, but composed of two subcomponents that decay with different rates. The narrow-line emission (50 kms^(−1) in FWHM) is near the systemic velocity of EX Lupi. These emission lines appear exclusively in v =1–0. The line widths translate to a characteristic orbiting radius of 0.4 AU. The broad-line component (FWZI ~ 150 km s^(−1)) is highly excited up to v ≤ 6. The line flux of the component decreases faster than the narrow-line emission. Simple modeling of the line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04–0.4 AU. The excitation state, the decay speed of the line flux, and the line profile indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event