Light-Induced Atomic Desorption for loading a Sodium Magneto-Optical Trap

We report studies of photon-stimulated desorption (PSD), also known as light-induced atomic desorption(LIAD), of sodium atoms from a vacuum cell glass surface used for loading a magneto-optical trap (MOT). Fluorescence detection was used to record the trapped atom number and the desorption rate. We observed a steep wavelength dependence of the desorption process above 2.6 eV photon energy, a result significant for estimations of sodium vapor density in the lunar atmosphere. Our data fit well to a simple model for the loading of the MOT dependent only on the sodium desorption rate and residual gas density. Up to 3.7x10^7 Na atoms were confined under ultra-high vacuum conditions, creating promising loading conditions for a vapor cell based atomic Bose-Einstein condensate of sodium.Comment: Sodium LIAD loaded MOT, 7 pages, 5 figures. Revised submitted manuscript with minor corrections, new data presented, Fig.5 change

Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift

We investigate the star formation history of the central regions of four Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact (MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than -17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B < 19.0 mag arcsec^-2) of this population. The observational data used were obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the HST/NICMOS first camera. We find evidence for multiple stellar populations. One of them is identified as the ionizing population, and the other one corresponds to the underlying stellar generation. The estimated masses of the inferred populations are compatible with the dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also indicate that the first episodes of star formation the presented LCBGs underwent happened between 5 and 7 Gyr ago. We compare the stellar populations found in LCBGs with the stellar populations present in bright, local HII galaxies, nearby spheroidal systems and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar populations of LCBGs are similar yet bluer to those of local HII galaxies. It is also the case that the passive color evolution of the LCBGs could convert them into local Spheroidal galaxies if no further episode of star formation takes place. Our results help to impose constraints on evolutionary scenarios for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with pdflatex. Contains png figure

Emission-Line Galaxy Surveys as Probes of the Spatial Distribution of Dwarf Galaxies. I. The University of Michigan Survey

Objective-prism surveys which select galaxies on the basis of line-emission are extremely effective at detecting low-luminosity galaxies and constitute some of the deepest available samples of dwarfs. In this study, we confirm that emission-line galaxies (ELGs) in the University of Michigan (UM) objective-prism survey (MacAlpine et al. 1977-1981) are reliable tracers of large-scale structure, and utilize the depth of the samples to examine the spatial distribution of low-luminosity (M$_{B} >$ -18.0) dwarfs relative to higher luminosity giant galaxies (M$_{B} \leq$ -18.0) in the Updated Zwicky Catalogue (Falco et al. 1999). New spectroscopic data are presented for 26 UM survey objects. We analyze the relative clustering properties of the overall starbursting ELG and normal galaxy populations, using nearest neighbor and correlation function statistics. This allows us to determine whether the activity in ELGs is primarily caused by gravitational interactions. We conclude that galaxy-galaxy encounters are not the sole cause of activity in ELGs since ELGs tend to be more isolated and are more often found in the voids when compared to their normal galaxy counterparts. Furthermore, statistical analyses performed on low-luminosity dwarf ELGs show that the dwarfs are less clustered when compared to their non-active giant neighbors. The UM dwarf samples have greater percentages of nearest neighbor separations at large values and lower correlation function amplitudes relative to the UZC giant galaxy samples. These results are consistent with the expectations of galaxy biasing.Comment: 17 pages, 4 tables, 10 figures. Accepted for publication in the Ap

Os tubarões hybodontiformes (Chondrichthyes: Euselachii) do Jurássico Superior de Torres Vedras, Portugal

ABSTRACT: In this work, the description and classification of a set of fossil shark tooth specimens, from the upper Kimmeridgian-lower Tithonian (Upper Jurassic) of Torres Vedras, was developed. The material, currently housed in the paleontological collection of Sociedade de História Natural, was collected on the surface of the marine deposits at the top of the Praia Azul Member, Lourinhã Formation, Lusitanian Basin. The attribution of the specimens to Hybodus cf. reticulatus, was based on the presence of the following most striking characteristics: a reticulated, spongy root, perpendicular to the crown; a completely to almost completely straight main cusp; several straight, well-defined, and parallel ridges that run from the base of the crown to about half of the height of the main cusp; and flat, well-defined cutting edges.RESUMO: No presente trabalho, fez-se a descrição e a classificação de um conjunto de espécimes de dentes fósseis de tubarão, do Kimmeridgiano superior-Tithoniano inferior (Jurássico Superior) de Torres Vedras. O material, atualmente sediado na coleção paleontológica da Sociedade de História Natural, foi colhido à superfície nos depósitos marinhos do topo do Membro da Praia Azul, Formação da Lourinhã, Bacia Lusitaniana. A atribuição dos espécimes a Hybodus cf. reticulatus, baseou-se na presença das seguintes características mais marcantes: raiz reticulada, esponjosa e perpendicular à coroa; cúspide principal totalmente ou quase totalmente estreita; várias pregas estreitas, bem definidas e paralelas entre si, que surgem desde a base da coroa até aproximadamente metade da altura da cúspide principal; e bordo cortante liso e bem definido.info:eu-repo/semantics/publishedVersio

UNDERWATER COMPARISON OF WAND AND 2D PLANE NONLINEAR CAMERA CALIBRATION METHODS

The purpose of this study was to compare two nonlinear camera calibration methods for 3D underwater motion analysis. The DVideo kinematic analysis system was used for underwater online data acquisition. The system consisted of two gen-locked Basler cameras working at 100Hz, with wide angle lenses that were enclosed in housings. The accuracy of both methods was compared in a dynamic rigid bar test. The mean absolute errors were 1.16mm for wand calibration, 1.20mm for 2D plane calibration using 8 control points and 0.73mm for 2D plane calibration using 16 control points. The results of both nonlinear camera calibration methods provided better underwater accuracy than all previous papers reported in literature. Both methods provided similar and highly accurate results, providing promising alternatives for underwater 3D motion analysis

Chemical Properties of Star-Forming Emission Line Galaxies at z=0.1 - 0.5

We measure oxygen and nitrogen abundances for 14 star-forming emission line galaxies (ELGs) at 0.11<z<0.5 using Keck/LRIS optical spectroscopy. The targets exhibit a range of metallicities from slightly metal-poor like the LMC to super-solar. Oxygen abundances of the sample correlate strongly with rest-frame blue luminosities. The metallicity-luminosity relation based on these 14 objects is indistinguishable from the one obeyed by local galaxies, although there is marginal evidence (1.1sigma) that the sample is slightly more metal-deficient than local galaxies of the same luminosity. The observed galaxies exhibit smaller emission linewidths than local galaxies of similar metallicity, but proper corrections for inclination angle and other systematic effects are unknown. For 8 of the 14 objects we measure nitrogen-to-oxygen ratios. Seven of 8 systems show evidence for secondary nitrogen production, with log(N/O)> -1.4 like local spirals. These chemical properties are inconsistent with unevolved objects undergoing a first burst of star formation. The majority of the ELGs are presently ~4 magnitudes brighter and ~0.5 dex more metal-rich than the bulk of the stars in well-known metal-poor dwarf spheroidals such as NGC 205 and NGC 185, making an evolution between some ELGs and metal-poor dwarf spheroidals improbable. However, the data are consistent with the hypothesis that more luminous and metal-rich spheroidal galaxies like NGC 3605 may become the evolutionary endpoints of some ELGs. [abridged]Comment: 41 pages, w/12 figures, uses AASTeX aaspp4.sty, psfig.sty; To appear in The Astrophysical Journa

The evolution of H{\sc ii} galaxies: Testing the bursting scenario through the use of self-consistent models

We have computed a series of realistic and self-consistent models of the emitted spectra of H{\sc ii} galaxies. Our models combine different codes of chemical evolution, evolutionary population synthesis and photoionization. The emitted spectrum of H{\sc ii} galaxies is reproduced by means of the photoionization code CLOUDY, using as ionizing spectrum the spectral energy distribution of the modelled H{\sc ii} galaxy, which in turn is calculated according to a Star Formation History (SFH) and a metallicity evolution given by a chemical evolution model that follows the abundances of 15 different elements. The contribution of emission lines to the broad-band colours is explicitly taken into account. The results of our code are compared with photometric and spectroscopic data of H{\sc ii} galaxies. Our technique reproduces observed diagnostic diagrams, abundances, equivalent width-colour and equivalent width-metallicity relations for local H{\sc ii} galaxies.Comment: 13 figures and 2 tables, accepted for publication in MNRAS Main Journa