A Morphological and Multicolor Survey for Faint QSOs in the Groth-Westphal Strip

Quasars representative of the populous faint end of the luminosity function are frustratingly dim with m~24 at intermediate redshift; moreover groundbased surveys for such faint QSOs suffer substantial morphological contamination by compact galaxies having similar colors. In order to establish a more reliable ultrafaint QSO sample, we used the APO 3.5-m telescope to take deep groundbased U-band CCD images in fields previously imaged in V,I with WFPC2/HST. Our approach hence combines multicolor photometry with the 0.1" spatial resolution of HST, to establish a morphological and multicolor survey for QSOs extending about 2 magnitudes fainter than most extant groundbased surveys. We present results for the "Groth-Westphal Strip", in which we identify 10 high likelihood UV-excess candidates having stellar or stellar-nucleus+galaxy morphology in WFPC2. For m(606)<24.0 (roughly B<24.5) the surface density of such QSO candidates is 420 (+180,-130) per square degree, or a surface density of 290 (+160,-110) per square degree with an additional V-I cut that may further exclude compact emission line galaxies. Even pending confirming spectroscopy, the observed surface density of QSO candidates is already low enough to yield interesting comparisons: our measures agree extremely well with the predictions of several recent luminosity function models.Comment: 29 pages including 6 tables and 7 figures. As accepted for publication in The Astronomical Journal (minor revisions

Cataclysmic Variables and Other Compact Binaries in the Globular Cluster NGC 362: Candidates from Chandra and HST

Highly sensitive and precise X-ray imaging from Chandra, combined with the superb spatial resolution of HST optical images, dramatically enhances our empirical understanding of compact binaries such as cataclysmic variables and low mass X-ray binaries, their progeny, and other stellar X-ray source populations deep into the cores of globular clusters. Our Chandra X-ray images of the globular cluster NGC 362 reveal 100 X-ray sources, the bulk of which are likely cluster members. Using HST color-magnitude and color-color diagrams, we quantitatively consider the optical content of the NGC 362 Chandra X-ray error circles, especially to assess and identify the compact binary population in this condensed-core globular cluster. Despite residual significant crowding in both X-rays and optical, we identify an excess population of H{\alpha}-emitting objects that is statistically associated with the Chandra X-ray sources. The X-ray and optical characteristics suggest that these are mainly cataclysmic variables, but we also identify a candidate quiescent low mass X-ray binary. A potentially interesting and largely unanticipated use of observations such as these may be to help constrain the macroscopic dynamic state of globular clusters.Comment: 6 pages, 6 figures, to appear in the proceedings of the conference "Binary Star Evolution: Mass Loss, Accretion, and Mergers," Mykonos, Greece, June 22-25, 201

A combined optical/infrared spectral diagnostic analysis of the HH1 jet

Complete flux-calibrated spectra covering the spectral range from 6000 A to 2.5 um have been obtained along the HH1 jet and analysed in order to explore the potential of a combined optical/near-IR diagnostic applied to jets from young stellar objects. Important physical parameters have been derived along the jet using various diagnostic line ratios. This multi-line analysis shows, in each spatially unresolved knot, the presence of zones at different excitation conditions, as expected from the cooling layers behind a shock front. In particular, a density stratification in the jet is evident from ratios of various lines of different critical density. In particular, [FeII] lines originate in a cooling layer located at larger distances from the shock front than that generating the optical lines, where the compression is higher and the temperature is declining. The derived parameters were used to measure the mass flux along the jet, adopting different procedures, the advantages and limitations of which are discussed. dM/dt is high in the initial part of the flow but decreases by about an order of magnitude further out. Conversely, the mass flux associated with the warm molecular material is low and does not show appreciable variations along the jet. We suggest that part of the mass flux in the external regions is not revealed in optical and IR lines because it is associated with a colder atomic component, which may be traced by the far-IR [O I]63 um line. Finally, we find that the gas-phase abundance of refractory species is lower than the solar value suggesting that a significant fraction of dust grains may still be present in the jet beam.Comment: Accepted on Astronomy & Astrophysic

Recipes for stellar jets: results of combined optical/infrared diagnostics

We examine the conditions of the plasma along a sample of 'classical' Herbig-Haro jets located in the Orion and Vela star forming regions, through combined optical-infrared spectral diagnostics. Our sample includes HH 111, HH 34, HH 83, HH 73, HH 24 C/E, HH 24 J, observed at moderate spatial/spectral resolution. The obtained spectra cover a wide wavelength range from 0.6-2.5 um, including many transitions from regions of different excitation conditions. This allows us to probe the density and temperature stratification which characterises the cooling zones behind the shock fronts along the jet. The derived physical parameters (such as the extinction, the electron density and temperature, the ionisation fraction, and the total density) are used to estimate the depletion onto dust grains of Calcium and Iron with respect to solar abundances. This turns out to be between 70% and 0% for Ca and ~90% for Fe, suggesting that the weak shocks present in the beams are not capable of completely destroying the dust grains. We then derive the mass flux rates (Mdot_jet is on average 5 10^-8 M_solar yr^-1) and the associated linear momentum fluxes. The latter are higher than, or of the same order as, those measured in the coaxial molecular flows, suggesting that the flows are jet driven. Finally, we discuss differences between jets in our sample.Comment: 19 pages, 15 figures, accepted by A&

A high-altitude balloon platform for determining exchange of carbon dioxide over agricultural landscapes

The exchange of carbon dioxide between the terrestrial biosphere and the atmosphere is a key process in the global carbon cycle. Given emissions from fossil fuel combustion and the appropriation of net primary productivity by human activities, understanding the carbon dioxide exchange of cropland agroecosystems is critical for evaluating future trajectories of climate change. In addition, human manipulation of agroecosystems has been proposed as a technique of removing carbon dioxide from the atmosphere via practices such as no-tillage and cover crops. We propose a novel method of measuring the exchange of carbon dioxide over croplands using a high-altitude balloon (HAB) platform. The HAB methodology measures two sequential vertical profiles of carbon dioxide mixing ratio, and the surface exchange is calculated using a fixed-mass column approach. This methodology is relatively inexpensive, does not rely on any assumptions besides spatial homogeneity (no horizontal advection) and provides data over a spatial scale between stationary flux towers and satellite-based inversion calculations. The HAB methodology was employed during the 2014 and 2015 growing seasons in central Illinois, and the results are compared to satellite-based NDVI values and a flux tower located relatively near the launch site in Bondville, Illinois. These initial favorable results demonstrate the utility of the methodology for providing carbon dioxide exchange data over a large (10–100 km) spatial area. One drawback is its relatively limited temporal coverage. While recruiting citizen scientists to perform the launches could provide a more extensive dataset, the HAB methodology is not appropriate for providing estimates of net annual carbon dioxide exchange. Instead, a HAB dataset could provide an important check for upscaling flux tower results and verifying satellite-derived exchange estimates

Low Luminosity X-ray Sources And Their Optical Counterparts In The Globular Cluster NGC 362: The Chandra/HST Perspective

Item does not contain fulltextAAS Meeting #213, 4 januari 200

Near-infrared, IFU spectroscopy unravels the bow-shock HH99B

Aims. We aim at characterising the morphology and the physical parameters governing the shock physics of the Herbig-Haro object HH99B. We obtained SINFONI-SPIFFI IFU spectroscopy ( R similar to 2000-4000) between 1.10 and 2.45 mu m detecting more than 170 emission lines, that, to a large extent, have never observed before in a Herbig-Haro object. Most of them come from ro-vibrational transitions of molecular hydrogen (upsilon(up) <= 7, E-up less than or similar to 38 000 K) and [ Fe II] ( Eup less than or similar to 30 000 K). In addition, we observed several hydrogen and helium recombination lines, along with fine-structure lines of ionic species. All the brightest lines appear resolved in velocity. Methods. Intensity ratios of ionic lines were compared with predictions of NLTE models to derive bi-dimensional maps of extinction and electron density, along with estimates of temperature, fractional ionisation, and atomic hydrogen post-shock density. The H-2 line intensities were interpreted in the framework of Boltzmann diagrams, from which we have derived extinction and temperature maps of the molecular gas. From the intensity maps of bright lines ( i.e. H-2 2.122 mu m and [ Fe II] 1.644 mu m), the kinematical properties of the shock(s) at work in the region were delineated. Finally, from selected [ Fe II] lines, constraints on the spontaneous emission coefficients of the 1.257, 1.321, and 1.644 mu m lines are provided. Results. Visual extinction variations up to 4 mag emerge, showing that the usual assumption of constant extinction could be critical. The highest AV is found at the bowhead ( AV similar to 4 mag) while diminishing along the flanks. The electron density increases from similar to 3 x 103 cm(-3) in the receding parts of the shock to similar to 6 x 103 cm(-3) in the apex, where we estimate a temperature of similar to 16 000 K from [ Fe II] line ratios. Molecular gas temperature is lower in the bow flanks ( T similar to 3000 K), then progressively increases toward the head up to T similar to 6000 K. In the same zone, we are able to derive the iron gas-phase abundance (similar to 60% of the solar value) from the [Fe II] 1.257/[P II] 1.187 line ratio, along with the hydrogen fractional ionisation ( up to 50% at the bowhead) and the atomic hydrogen post-shock gas density (similar to 1 x 104 cm(-3)). The kinematical properties derived for the molecular gas substantially confirm earlier ones, while new information ( e. g. vshock similar to 115 km s(-1)) is provided for the shock component responsible for the ionic emission. We also provide an indirect measure of the H-2 breakdown speed ( between 70 and 90 kms(-1)) and compute the inclination angle with respect to the line of sight. The map parameters, along with images of the observed line intensities, will be used to put stringent constraints on up-to-date shock models