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Downes J.J.,National Autonomous University of Mexico | Briceno C.,Cerro Tololo Interamerican Observatory | Mateu C.,National Autonomous University of Mexico | Vivas A.K.,Cerro Tololo Interamerican Observatory | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present the results of a survey of the low-mass star and brown dwarf population of the 25 Orionis group. Using optical photometry from the CIDA (Centro de Investigaciones de Astronomía 'Francisco J. Duarte', Mérida, Venezuela) Deep Survey of Orion, near-IR photometry from the Visible and Infrared Survey Telescope for Astronomy and low-resolution spectroscopy obtained with Hectospec at the MMT telescope, we selected 1246 photometric candidates to low-mass stars and brown dwarfs with estimated masses within 0.02 ≲ M/M ≲ 0.8 and spectroscopically confirmed a sample of 77 low-mass stars as new members of the cluster with a mean age of ~7 Myr. We have obtained a system initial mass function of the group that can be well described by either a Kroupa power-law function with indices α3 = -1.73 ± 0.31 and α2 = 0.68 ± 0.41 in the mass ranges 0.03 ≤ M/M ≤ 0.08 and 0.08 ≤ M/M ≤ 0.5, respectively, or a Scalo lognormal function with coefficients mc = 0.21+0.02-0.02 and σ = 0.36 ± 0.03 in the mass range 0.03 ≤ M/M ≤ 0.8. From the analysis of the spatial distribution of this numerous candidate sample, we have confirmed the east-west elongation of the 25 Orionis group observed in previous works, and rule out a possible southern extension of the group. We find that the spatial distributions of low-mass stars and brown dwarfs in 25 Orionis are statistically indistinguishable. Finally, we found that the fraction of brown dwarfs showing IR excesses is higher than for low-mass stars, supporting the scenario in which the evolution of circumstellar discs around the least massive objects could be more prolonged. © 2014 The Authors.


Trichas M.,Harvard - Smithsonian Center for Astrophysics | Green P.J.,Harvard - Smithsonian Center for Astrophysics | Silverman J.D.,University of Tokyo | Aldcroft T.,Harvard - Smithsonian Center for Astrophysics | And 19 more authors.
Astrophysical Journal, Supplement Series | Year: 2012

From optical spectroscopy of X-ray sources observed as part of the Chandra Multi-wavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-up using the FLWO/1.5m, SAAO/1.9m, WIYN 3.5m, CTIO/4m, KPNO/4m, Magellan/6.5m, MMT/6.5m, and Gemini/8m telescopes, and from archival Sloan Digital Sky Survey (SDSS) spectroscopy. We classify the optical counterparts as 50% broad-line active galactic nuclei (AGNs), 16% emission line galaxies, 14% absorption line galaxies, and 20% stars. We detect QSOs out to z ∼ 5.5 and galaxies out to z ∼ 3. We have compiled extensive photometry, including X-ray (ChaMP), ultraviolet (GALEX), optical (SDSS and ChaMP-NOAO/MOSAIC follow-up), near-infrared (UKIDSS, Two Micron All Sky Survey, and ChaMP-CTIO/ISPI follow-up), mid-infrared (WISE), and radio (FIRST and NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGNs and starburst components where both are present. While 58% of X-ray Seyferts (10 42 erg s -1 < L 2 - 10 keV <10 44ergs -1) require a starburst event (>5% starburst contribution to bolometric luminosity) to fit observed photometry only 26% of the X-ray QSO (L 2 - 10 keV >10 44ergs -1) population appear to have some kind of star formation contribution. This is significantly lower than for the Seyferts, especially if we take into account torus contamination at z > 1 where the majority of our X-ray QSOs lie. In addition, we observe a rapid drop of the percentage of starburst contribution as X-ray luminosity increases. This is consistent with the quenching of star formation by powerful QSOs, as predicted by the merger model, or with a time lag between the peak of star formation and QSO activity. We have tested the hypothesis that there should be a strong connection between X-ray obscuration and star formation but we do not find any association between X-ray column density and star formation rate both in the general population or the star-forming X-ray Seyferts. Our large compilation also allows us to report here the identification of 81 X-ray Bright Optically inactive Galaxies, 78 z > 3 X-ray sources, and eight Type-2 QSO candidates. Also, we have identified the highest redshift (z = 5.4135) X-ray-selected QSO with optical spectroscopy. © 2012. The American Astronomical Society. All rights reserved..


News Article | December 1, 2015
Site: www.rdmag.com

Prof. Robert Berrington, of Ball State Univ., was in third grade the first time he peered through a telescope. Inspired by the deep-sky objects described in magazines, such as Sky & Telescope, he purchased a refractor telescope, and searched the sky, setting his sights on planets and the moon. Unfortunately, the telescope wasn’t the best quality and the deep-sky objects that held his attention eluded him. “Fortunately, I knew a local high school physics teacher who was selling a 6-in (Criterion RV-6 Dynascope) reflector telescope for cheap, which I promptly acquired,” says Berrington in an interview with R&D Magazine. “It was really through this telescope that I would say was my first real view through a telescope. I quickly learned the ropes of finding these deep-sky objects, and was hooked from then on.” Since 2008, Berrington has worked as an astronomer in Ball State Univ.’s Dept. of Physics and Astronomy, teaching courses from Introduction to Astrophysics to Stellar Evolution, Galaxies and Cosmology. His research interests include monitoring and modeling short-period eclipsing variable stars, and studying the structure and dynamics of elliptical galaxies. Now, Berrington and his students can watch the skies in northern Africa without leaving their campus in Muncie, Ind., with the addition of the Jacobus Kapteyn telescope to their astronomical tool belt. Berrington recently attended the telescope’s dedication ceremony in October. “The Canary Islands are well-suited for an observatory largely because they are isolated,” he says. Located on an island in the Atlantic Ocean, the new telescope is distant from large population centers that usually shroud the night sky with light pollution, an inhibitor to astronomical study. The “newly acquired telescope is a 1.0-m telescope located on La Palma, Spain, off the west coast of Morocco, Africa.” The new telescope is maintained and operated by the Southeastern Association for Research in Astronomy (SARA), which is comprised of 13 institutions, including Ball State Univ. Altogether, the consortium will operate three telescopes once the Kapetyn telescope becomes available at the end of the year. The other two telescopes are located in Kitt Peak National Observatory (KPNO), about an hour west of Tucson, Ariz.., by car, and a 0.6-m telescope located at the Cerro Tololo Interamerican Observatory in Chile. Due to the new telescope’s eastwardly location, “the night time for the La Palma telescope differs from the nighttime here in Muncie. It occurs earlier, or approximately 5 hrs earlier,” says Berrington. “This means for classes that occur in the afternoon here in Muncie (after ~1PM), it is nighttime on La Palma, and actual nighttime observations can occur during the scheduled classroom time. This was not possible with the two prior telescopes operated by the SARA Consortium.” Since much astronomy observation deals with time series analysis of a celestial object’s brightness, Berrington says the new telescope only adds more night for the students’ observations. “We can start our observations of an object on La Palma, and transition those observations from La Palma to KPNO when it becomes night time in Arizona (approximately 7 hrs later),” he says. “This allows us to extend the time frame of continuous monitoring from the traditional limit of approximately 12 hrs to approximately 19 hrs every 24-hr period.” All SARA telescopes are capable of being controlled from anywhere on the planet with an internet connection, and the university is given 55 nights per year of access for instructional and research purposes. “These telescopes give today’s students unprecedented access to professional quality sites with minimal interruption to their instruction,” Berrington says.


Navarrete J.C.S.,University of La Serena | Navarrete J.C.S.,Cerro Tololo InterAmerican Observatory | Roman-Lopes A.,University of La Serena | Santos F.P.,The Interdisciplinary Center | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present a polarimetric study of the RCW121 star-forming region to derive the orientation of the sky-projected magnetic field component traced by the polarization vectors, the morphology of which tends to follow the cloud's structure. Individual polarization-angle values are consistent across the different bands, having a broad distribution towards the RCW121 H II region. We estimate the corresponding magnetic field orientation in the H II region to have a mean value of -12° ± 7°. RCW121 shows an elongated shape in the same direction as the magnetic field orientation, which may be evidence that magnetic pressure opposes the H II region expansion. Serkowski's relation was used to determine individual values of the total-to-selective extinction ratio (RV) distribution and a weighted mean value of RV = 3.17 ± 0.05. We derive a foreground component of the polarization degree that is consistent with the literature value for this Galactic region. © 2016 The Authors.


Duffau S.,University of Heidelberg | Vivas A.K.,Cerro Tololo Interamerican Observatory | Zinn R.,Yale University | Mendez R.A.,University of Chile | Ruiz M.T.,University of Chile
Astronomy and Astrophysics | Year: 2014

To explore the complex halo substructure that has been reported in the direction of the Virgo constellation, radial velocities and metallicities have been measured for 82 RR Lyrae stars (RRLS) that were identified by the QUEST survey. These stars are distributed over 90 square degrees of the sky, and lie from 4 to 23 kpc from the Sun. Using an algorithm for finding groups in phase space and modeling the smooth halo component in the region, we identified the 5 most significant RRLS groups, some of which were previously known or suspected. We have examined the SEKBO and the Catalina catalog of RRLS (with available spectroscopic measurements), as well as the bright QUEST RRLS sample, the catalog of Red Giant stars from the Spaghetti survey, and three recent catalogs of blue horizontal branch (BHB) stars, for stars that may be related to the QUEST RRLS groups. The most significant group of RRLS is the Virgo stellar stream (VSS) identified here as group A, which is composed of at least 10 RRLS and 3 BHB stars. It has a mean distance of 19.6 kpc and a mean radial velocity Vgsr = 128 km s-1, as estimated from its RRLS members. With the revised velocities reported here, there is no longer an offset in velocity between the RRLS in the VSS and the prominent peak in the velocities of main-sequence turnoff stars reported by other researchers in the same direction and at a similar distance (known as S297+63-20.5). The location in phase space of two other groups (F and H) suggests a possible connection with the VSS, which cannot be discarded at this point, although the turnoff colors of the VSS and group H, as identified from other works, suggest they might be composed of different populations. Two more groups, B and D, are found at mean distances of 19.0 and 5.7 kpc, and mean radial velocities of Vgsr = -94 and 32 km s-1. The latter is the more numerous in terms of total members, as well as the more extended in RA. A comparison with the latest model of the disruption of the Sagittarius dwarf, indicates that none of the above groups is related to it. Rather than being the result of a single accretion event, the excess of stars observed in Virgo appears to be composed of several halo substructures along the same line of sight. © ESO, 2014.


Dzib S.A.,Max Planck Institute for Radio Astronomy | Loinard L.,National Autonomous University of Mexico | Rodriguez L.F.,National Autonomous University of Mexico | Rodriguez L.F.,King Abdulaziz University | And 11 more authors.
Astrophysical Journal | Year: 2015

We present a multi-epoch radio study of the Taurus-Auriga star-forming complex made with the Karl G. Jansky Very Large Array at frequencies of 4.5 GHz and 7.5 GHz. We detect a total of 610 sources, 59 of which are related to young stellar objects (YSOs) and 18 to field stars. The properties of 56% of the young stars are compatible with non-thermal radio emission. We also show that the radio emission of more evolved YSOs tends to be more non-thermal in origin and, in general, that their radio properties are compatible with those found in other star-forming regions. By comparing our results with previously reported X-ray observations, we notice that YSOs in Taurus-Auriga follow a Güdel-Benz relation with κ = 0.03, as we previously suggested for other regions of star formation. In general, YSOs in Taurus-Auriga and in all the previous studied regions seem to follow this relation with a dispersion of 1 dex. Finally, we propose that most of the remaining sources are related with extragalactic objects but provide a list of 46 unidentified radio sources whose radio properties are compatible with a YSO nature. © 2015. The American Astronomical Society. All rights reserved.


Ortiz-Leon G.N.,National Autonomous University of Mexico | Loinard L.,National Autonomous University of Mexico | Loinard L.,Max Planck Institute for Radio Astronomy | Mioduszewski A.J.,U.S. National Radio Astronomy Observatory | And 13 more authors.
Astrophysical Journal | Year: 2015

We present deep (∼17 μJy) radio continuum observations of the Serpens molecular cloud, the Serpens south cluster, and the W40 region obtained using the Very Large Array in its A configuration. We detect a total of 146 sources, 29 of which are young stellar objects (YSOs), 2 of which are BV stars, and 5 more of which are associated with phenomena related to YSOs. Based on their radio variability and spectral index, we propose that about 16 of the remaining 110 unclassified sources are also YSOs. For approximately 65% of the known YSOs detected here as radio sources, the emission is most likely non-thermal and related to stellar coronal activity. As also recently observed in Ophiuchus, our sample of YSOs with X-ray counterparts lies below the fiducial Güdel & Benz relation. Finally, we analyze the proper motions of nine sources in the W40 region. This allows us to better constrain the membership of the radio sources in the region. © 2015. The American Astronomical Society. All rights reserved.


Kounkel M.,University of Michigan | Hartmann L.,University of Michigan | Loinard L.,National Autonomous University of Mexico | Loinard L.,Max Planck Institute for Radio Astronomy | And 11 more authors.
Astrophysical Journal | Year: 2014

We present results from a high-sensitivity (60 μJy), large-scale (2.26 deg2) survey obtained with the Karl G. Jansky Very Large Array as part of the Gould's Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5 GHz, respectively. Of these, 148 are associated with previously known young stellar objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous results from the Gould's Belt Survey. Our detections provide target lists for follow-up Very Long Baseline Array radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes. © 2014. The American Astronomical Society. All rights reserved..


James D.J.,Cerro Tololo InterAmerican Observatory | Aarnio A.N.,University of Michigan | Richert A.J.W.,Pennsylvania State University | Cargile P.A.,Harvard - Smithsonian Center for Astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present the results of an optical photometry and high-resolution spectroscopy campaign for a modest sample of X-ray selected stars in the Chamaeleon and Rho Ophiuchus star-forming regions. With R~ 50 000 optical spectra, we establish kinematic membership of the parent association and confirm stellar youth for each star in our sample. With the acquisition of new standardized BVIc photometry, in concert with near-infrared data from the literature, we derive age and mass from stellar positions in model-dependent Hertzsprung-Russell diagrams. We compare isochronal ages derived using colour-dependent extinction values finding that, within error bars, ages are the same irrespective of whether E(B - V), E(V - Ic), E(J - H) or E(H - K) is used to establish extinction, although model ages tend to be marginally younger for redder Ecolour values. For Cham I and η Cham members, we derive ages of ≲5-6 Myr, whereas our three η Cha candidates are more consistent with a ≳25 Myr post-T Tauri star population. In Rho Ophiuchus, most stars in our sample have isochronal ages <10 Myr. Five objects show evidence of strong infrared excess (Av > 5) in the Two Micron All Sky Survey colour-colour diagram, however in terms of Ha emission, all stars except RXJ1625.6-2613 are consistent with being weak-lined T-Tauri stars. Spectral energy distributions (SEDs) over the range ⋍4000Å <λ < 1000 μm, show that only one Chamaeleon star (RXJ1112.7 -7637) and three Rho Ophiuchus stars (ROXR1 13, RXJ1625.6-2613 & RXJ1627.1-2419) reveal substantial departures from a bare photosphere. © 2016 The Authors.


Tokovinin A.,Cerro Tololo Interamerican Observatory
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes | Year: 2013

The SOAR adaptive module (SAM) is going through science verification and is offered in shared risk in 2013B. It is a GLAO instrument with a UV Rayleigh laser to improve image quality in the visible. The resolution in closed loop reaches 0.25′′ in the I band (typical 0.4′′ in I, 0.5′′ in V). Substantial gain over open-loop resolution was reached on 6 nights out of 11 in 2012-2013, under calm free-atmosphere conditions. The compensation is uniform over the 3-arcmin. field. We discuss operational aspects of SAMand its potential science programs. Critical evaluation of the design might be of interest to other AO instruments.We stress the need to provide GLAOcorrection at visible wavelengths for ELTs and the relevance of SAM from this perspective.

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