106 research outputs found

    Really Cool Stars and the Star Formation History at the Galactic Center

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    We present R=550 to 1200 near infrared H and K spectra for a magnitude limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~ 5 pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the Hertzsprung--Russell (HRD) diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC. We find (1) roughly 75% of the stars formed in the central few pc are older than 5 Gyr; (2) the star formation rate (SFR) is variable over time, with a roughly 4 times higher star formation rate in the last 100 Myr compared to the average SFR; (3) our model can only match dynamical limits on the total mass of stars formed by limiting the IMF to masses above 0.7 M‚äô_\odot. This could be a signature of mass segregation or of the bias toward massive star formation from the unique star formation conditions in the GC; (4) blue supergiants account for 12 % of the total sample observed, and the ratio of red to blue supergiants is roughly 1.5; (5) models with isochrones with [Fe/H] = 0.0 over all ages fit the stars in our HRD better than models with lower [Fe/H] in the oldest age bins, consistent with the finding of Ramirez et al. (2000) that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].Comment: ApJ, accepted. Latex, 65 pages including 19 figure

    SysML model of exoplanet archive functionality and activities

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    The NASA Exoplanet Archive is an online service that serves data and information on exoplanets and their host stars to help astronomical research related to search for and characterization of extra-solar planetary systems. In order to provide the most up to date data sets to the users, the exoplanet archive performs weekly updates that include additions into the database and updates to the services as needed. These weekly updates are complex due to interfaces within the archive. I will be presenting a SysML model that helps us perform these update activities in a weekly basis

    Self-efficacy of English-Spanish Translation students in Chilean higher education institutions

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    El presente trabajo corresponde a un estudio exploratorio cuantitativo-cualitativo, de dise√Īo secuencial-explicativo, cuyo objetivo es comprender a nivel a macro y micro la autoeficacia de los estudiantes de la carrera de Traducci√≥n ingl√©s-espa√Īol de instituciones chilenas. Para el logro de dicho objetivo, en una primera fase cuantitativa, se aplic√≥ la Escala de Autoeficacia General a 160 estudiantes entre todas las instituciones de educaci√≥n superior chilenas que imparten la carrera profesional de traducci√≥n ingl√©s-espa√Īol y, para la fase cualitativa subsecuente, se recurri√≥ a una triangulaci√≥n de las t√©cnicas de protocolo verbal retrospectivo y entrevista en profundidad a 3 participantes de distintas universidades de la V regi√≥n de Chile. Los resultados indican que la Escala de Autoeficacia General, a pesar de su frecuente uso en el campo de los estudios de traducci√≥n, presenta muy poca especificidad para medir la autoeficacia en estudiantes de traducci√≥n ingl√©s-espa√Īol. Asimismo, los resultados de la etapa cualitativa indican que los factores que tienen mayor influencia en la autoeficacia de los estudiantes de traducci√≥n ingl√©s-espa√Īol corresponden al manejo disciplinar que estos presentan en las distintas √°reas al momento de traducir, al rol que tienen sus docentes y compa√Īeros de curso, y a los distintos estados fisiol√≥gicos y emocionales que experimentan.This quantitative-qualitative exploratory study, of sequential-explanatory design, understands at a macro and micro level self-efficacy of English-Spanish Translation program students of Chilean institutions. In a first quantitative phase, the Escala de Autoeficacia General was applied to 160 students among all the Chilean higher education institutions that teach the professional English-Spanish translation program, and for the subsequent qualitative phase, a triangulation of the Retrospective verbal protocol techniques and in-depth interview was conducted to 3 participants from different universities in the V region of Chile. The results indicate that the General Self-Efficacy Scale, despite its frequent use in the field of translation studies, has very little specificity to measure self-efficacy in translation students and, among the factors that have the greatest impact on the self-efficacy of English-Spanish translation students, we can find knowledge in different areas, teachers and classmates‚Äô role, and physiological and emotional states

    Planetary Candidates Observed by Kepler. VI. Planet Sample from Q1--Q16 (47 Months)

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    We present the sixth catalog of Kepler candidate planets based on nearly four years of high precision photometry. This catalog builds on the legacy of previous catalogs released by the Kepler project and includes 1493 new Kepler Objects of Interest (KOIs) of which 554 are planet candidates, and 131 of these candidates have best-fit radii > 1.5 R_‚äē. This brings the total number of KOIs and planet candidates to 7348 and 4175 respectively. We suspect that many of these new candidates at the low signal-to-noise ratio limit may be false alarms created by instrumental noise, and discuss our efforts to identify such objects. We re-evaluate all previously published KOIs with orbital periods of > 50 days to provide a consistently vetted sample that can be used to improve planet occurrence rate calculations. We discuss the performance of our planet detection algorithms, and the consistency of our vetting products. The full catalog is publicly available at the NASA Exoplanet Archive

    Non-Acceleration of Sgr A*: Implications for Galactic Structure

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    We show that observations by Backer and collaborators over the past two decades constrain the time derivative of the proper motion of Sgr A* to be less than 0.14 mas yr^{-2}. Using this result and a preliminary measurement by Eckart and Genzel of sigma ~500 kms for the velocity dispersion of the star cluster within 0.2" of Sgr A*, we derive the following implications. First, if the nuclear star cluster is dominated by a massive black hole, then either Sgr A* is that black hole or it orbits the black hole with a radius less than 3 AU. Second, even if the star cluster does not contain a massive black hole, Sgr A* is constrained to move slower than 20 kms (1 sigma) relative to the center of mass of the cluster. The Galactocentric distance is therefore R_0=7.5 +/- 0.7 kpc, independent of the nature of Sgr A*. These error bars could be substantially reduced by future observations. If they are, it will also be possible to probe the motion of the nuclear star cluster relative to the center of mass of the Galaxy at the ~4 kms level.Comment: 9 pages, no figure

    Adición de la ceniza de corteza de pino para estabilizar la subrasante de la carretera CA-1272 - EMP PE-8A - Granja Porcón, Cajamarca 2022

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    La presente investigaci√≥n tuvo como finalidad demostrar la influencia de la adici√≥n de ceniza de corteza de pino en la estabilizaci√≥n de la subrasante, en la carretera CA-1272 - EMP PE-8A - Granja Porc√≥n. Se empleo la metodolog√≠a tipo aplicada con enfoque cuantitativo, a su vez con un nivel de investigaci√≥n explicativa con dise√Īo experimental del tipo cuasi ‚Äď experimental, teniendo como poblaci√≥n un kil√≥metro de poblaci√≥n desde la progresiva 4+000 a la 5+000 (tres calicatas), con la muestra de una calicata (la m√°s desfavorable), un muestreo no probabil√≠stico y t√©cnica de instrumento por medio de las normas t√©cnica peruana, reglamentos nacionales e internacionales. Se tuvo resultados favorables, as√≠ mismo para el ensayo de CBR el suelo patr√≥n paso de un 2% a un 4.4% de la M.D.S al 95%, con la dosificaci√≥n de 6%, as√≠ tambi√©n hubo un desenlace benigno con respecto al ensayo de humedad optima y m√°xima densidad seca d√°ndonos un suelo patr√≥n de 28% con 1.337 g/cm3 y con la ceniza de corteza de pino en un 2% de dosificaci√≥n a un 24% y 1.356 g/cm3. Concluyendo de que existe una mejor√≠a al contar con el aditivo de ceniza de corteza de pino en las dosificaciones de 2%, 4% y 6%

    Planetary Candidates Observed by Kepler. VII. The First Fully Uniform Catalog Based on the Entire 48-month Data Set (Q1‚ÄďQ17 DR24)

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    We present the seventh Kepler planet candidate (PC) catalog, which is the first catalog to be based on the entire, uniformly processed 48-month Kepler data set. This is the first fully automated catalog, employing robotic vetting procedures to uniformly evaluate every periodic signal detected by the Q1‚ÄďQ17 Data Release 24 (DR24) Kepler pipeline. While we prioritize uniform vetting over the absolute correctness of individual objects, we find that our robotic vetting is overall comparable to, and in most cases superior to, the human vetting procedures employed by past catalogs. This catalog is the first to utilize artificial transit injection to evaluate the performance of our vetting procedures and to quantify potential biases, which are essential for accurate computation of planetary occurrence rates. With respect to the cumulative Kepler Object of Interest (KOI) catalog, we designate 1478 new KOIs, of which 402 are dispositioned as PCs. Also, 237 KOIs dispositioned as false positives (FPs) in previous Kepler catalogs have their disposition changed to PC and 118 PCs have their disposition changed to FPs. This brings the total number of known KOIs to 8826 and PCs to 4696. We compare the Q1‚ÄďQ17 DR24 KOI catalog to previous KOI catalogs, as well as ancillary Kepler catalogs, finding good agreement between them. We highlight new PCs that are both potentially rocky and potentially in the habitable zone of their host stars, many of which orbit solar-type stars. This work represents significant progress in accurately determining the fraction of Earth-size planets in the habitable zone of Sun-like stars. The full catalog is publicly available at the NASA Exoplanet Archive

    Optimization of autohydrolysis conditions to extract antioxidant phenolic compounds from spent coffee grounds

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    Autohydrolysis, which is an eco-friendly technology that employs only water as extraction solvent, was used to extract antioxidant phenolic compounds from spent coffee grounds (SCG). Experimental assays were carried out using different temperatures (160 to 200 ¬įC), liquid/solid ratios (5 to 15 ml/g SCG) and extraction times (10 to 50 min) in order to determine the conditions that maximize the extraction results. The optimum conditions to produce extracts with high content of phenolic compounds (40.36 mg GAE/g SCG) and high antioxidant activity (FRAP = 69.50 mg Fe(II)/g SCG, DPPH = 28.15 mg TE/g SCG, ABTS = 31.46 mg TE/g SCG, and TAA = 66.21 mg -TOC/g SCG) consisted in using 15 ml water/g SCG, at 200 ¬įC during 50 min. Apart from being a green technology, autohydrolysis under optimized conditions was demonstrated to be an efficient method to extract antioxidant phenolic compounds from SCG.This work was supported by the Science and Technology Foundation of Portugal (FCT - grant SFRH/BD/80948/2011); the Strategic Project PEst-OE/EQB/LA0023/2013; and the Project ‚ÄúBio-Ind -Biotechnology and Bioengineering for improved Industrial and Agro-Food processes‚ÄĚ, REF. NORTE-07-0124-FEDER-000028 cofunded by the Programa Operacional Regional do Norte (ON.2 e O Novo Norte), QREN, FEDER

    Accurate Coordinates and 2MASS Cross-IDs for (Almost) All Gliese Catalog Stars

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    We provide precise J2000, epoch 2000 coordinates and cross-identifications to sources in the 2MASS point source catalog for nearly all stars in the Gliese, Gliese and Jahreiss, and Woolley catalogs of nearby stars. The only Gliese objects where we were not successful are two Gliese sources that are actually QSOs, two proposed companions to brighter stars which we believe do not exist, four stars included in one of the catalogs but identified there as only optical companions, one probable plate flaw, and two stars which simply remain un-recovered. For the 4251 recovered stars, 2693 have coordinates based on Hipparcos positions, 1549 have coordinates based on 2MASS data, and 9 have positions from other astrometric sources. All positions have been calculated at epoch 2000 using proper motions from the literature, which are also given here.Comment: accepted to PASP, Full version of Table 1 available electronicall

    Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy

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    We present chemical abundances in a sample of luminous cool stars located within 30 pc of the Galactic center. Abundances of carbon, nitrogen, oxygen, calcium, and iron were derived from high-resolution infrared spectra in the H and K bands. The abundance results indicate that both [O/Fe] and [Ca/Fe] are enhanced, respectively, by averages of +0.2 and +0.3 dex, relative to either the Sun or the Milky Way disk at near-solar Fe abundances. The Galactic center stars show a nearly uniform and nearly solar iron abundance. The mean value of A(Fe) = 7.59 ¬Ī 0.06 agrees well with previous work. The total range in Fe abundance among Galactic center stars, 0.16 dex, is significantly narrower than the iron abundance distributions found in the literature for the older bulge population. Our snapshot of the current-day Fe abundance within 30 pc of the Galactic center samples stars with an age less than 1 Gyr; a larger sample in time (or space) may find a wider spread in abundances
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