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Calvet N.,University of Michigan | Hartmann L.,University of Michigan | Muzerolle J.,Space Telescope Institute | Gutermuth R.,Smith College | Stauffer J.,Spitzer Science Center
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2011

We are carrying out a study of disk populations in young stellar regions spanning an age range from few Myr to ∼ 10 Myr. Using the unprecedented sensitivity and spatial resolution provided by the Spitzer Space Telescope with its instruments IRAC and MIPS, we have identified and characterized protoplanetary disks around young stellar objects (spanning a wide range of stellar masses) in several stellar groups. We find that for stellar groups of ∼ 5 Myr or older the disk frequency in intermediate mass stars (with spectral types from late B to early F) is higher than for low mass stars (with spectral types K and M). This is in contradiction with the observed trend for primordial disks evolution, in which stars with higher stellar masses dissipate their primordial disks faster. At 3 Myr the disk frequency in intermediate mass stars is still lower than for low mass stars indicating that second generation dusty disks start to dominate the disk population at 5 Myr for intermediate mass stars. This result agrees with models of evolution of solids in the region of the disk where icy object form, which suggest that at 5-10 Myr collisions start to produce large amount of dust during the transition from runaway to oligarchic growth and then dust production peaks at 10-20 Myr, when objects reach their maximum sizes. © 2011: Instituto de Astronomía.

Tsapras Y.,University of Heidelberg | Tsapras Y.,Las Cumbres Observatory Global Telescope Network | Hundertmark M.,Kobnhavns University | Wyrzykowski L.,University of Warsaw | And 21 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We use six years (2003-2008) of Optical Gravitational Lensing Experiment-III microlensing observations to derive the survey detection efficiency for a range of planetary masses and projected distances from the host star. We perform an independent analysis of the microlensing light curves to extract the event parameters and compute the planet detection probability given the data. 2433 light curves satisfy our quality selection criteria and are retained for further processing. The aggregate of the detection probabilities over the range explored yields the expected number of microlensing planet detections. We employ a Galactic model to convert this distribution from dimensionless to physical units, α/au and M⊕. The survey sensitivity to small planets is highest in the range 1-4 au, shifting to slightly larger separations for more massive ones. © 2016 The Authors.

Rhoads J.E.,Arizona State University | Malhotra S.,Arizona State University | Allam S.,Space Telescope Institute | Carilli C.,U.S. National Radio Astronomy Observatory | And 10 more authors.
Astrophysical Journal | Year: 2014

We report on two regularly rotating galaxies at redshift z 2, using high-resolution spectra of the bright [C II] 158 μm emission line from the HIFI instrument on the Herschel Space Observatory. Both SDSS090122.37+181432.3 ("S0901") and SDSSJ120602.09+514229.5 ("the Clone") are strongly lensed and show the double-horned line profile that is typical of rotating gas disks. Using a parametric disk model to fit the emission line profiles, we find that S0901 has a rotation speed of vsin (i) 120 ± 7 km s-1 and a gas velocity dispersion of σ g < 23 km s -1 (1σ). The best-fitting model for the Clone is a rotationally supported disk having vsin (i) 79 ± 11 km s-1 and σ g ≲ 4 km s-1 (1σ). However, the Clone is also consistent with a family of dispersion-dominated models having σ g = 92 ± 20 km s-1. Our results showcase the potential of the [C II] line as a kinematic probe of high-redshift galaxy dynamics: [C II] is bright, accessible to heterodyne receivers with exquisite velocity resolution, and traces dense star-forming interstellar gas. Future [C II] line observations with ALMA would offer the further advantage of spatial resolution, allowing a clearer separation between rotation and velocity dispersion. © 2014. The American Astronomical Society. All rights reserved..

Espaillat C.,Harvard - Smithsonian Center for Astrophysics | Ingleby L.,University of Michigan | Furlan E.,National Optical Astronomy Observatory | Furlan E.,California Institute of Technology | And 6 more authors.
Astrophysical Journal | Year: 2012

Two decades ago "transitional disks" (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC2068 and IC348. One group has a "dip" in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects "transitional disks" and "pre-transitional disks" (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term "transitional" only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks. © 2012 The American Astronomical Society. All rights reserved.

Espaillat C.,Harvard - Smithsonian Center for Astrophysics | D'Alessio P.,National Autonomous University of Mexico | Nagel E.,University of Guanajuato | Luhman K.L.,Pennsylvania State University | And 4 more authors.
Astrophysical Journal | Year: 2010

In the past few years, several disks with inner holes that are relatively empty of small dust grains have been detected and are known as transitional disks. Recently, Spitzer has identified a new class of "pre-transitional disks" with gaps based on near-infrared photometry and mid-infrared spectra; these objects have an optically thick inner disk separated from an optically thick outer disk by an optically thin disk gap. A near-infrared spectrum provided the first confirmation of a gap in the pre-transitional disk of LkCa 15 by verifying that the near-infrared excess emission in this object was due to an optically thick inner disk. Here, we investigate the difference between the nature of the inner regions of transitional and pre-transitional disks using the same veiling-based technique to extract the near-infrared excess emission above the stellar photosphere. However, in this work we use detailed disk models to fit the excess continua as opposed to the simple blackbody fits previously used. We show that the near-infrared excess emission of the previously identified pre-transitional disks of LkCa 15 and UX Tau A in the Taurus cloud as well as the newly identified pre-transitional disk of ROX 44 in Ophiuchus can be fit with an inner disk wall located at the dust destruction radius. We also present detailed modeling of the broadband spectral energy distributions of these objects, taking into account the effect of shadowing by the inner disk on the outer disk, but considering the finite size of the star, unlike other recent treatments. The near-infrared excess continua of these three pre-transitional disks, which can be explained by optically thick inner disks, are significantly different from that of the transitional disks of GM Aur, whose near-infrared excess continuum can be reproduced by emission from sub-micron-sized optically thin dust, and DM Tau, whose near-infrared spectrum is consistent with a disk hole that is relatively free of small dust. The structure of pre-transitional disks may be a sign of young planets forming in these disks and future studies of pre-transitional disks will provide constraints to aid in theoretical modeling of planet formation. © 2010. The American Astronomical Society.

News Article | March 1, 2017

New Haven, Conn. - A Yale-led team has produced one of the highest-resolution maps of dark matter ever created, offering a detailed case for the existence of cold dark matter -- sluggish particles that comprise the bulk of matter in the universe. The dark matter map is derived from Hubble Space Telescope Frontier Fields data of a trio of galaxy clusters that act as cosmic magnifying glasses to peer into older, more distant parts of the universe, a phenomenon known as gravitational lensing. Yale astrophysicist Priyamvada Natarajan led an international team of researchers that analyzed the Hubble images. "With the data of these three lensing clusters we have successfully mapped the granularity of dark matter within the clusters in exquisite detail," Natarajan said. "We have mapped all of the clumps of dark matter that the data permit us to detect, and have produced the most detailed topological map of the dark matter landscape to date." Scientists believe dark matter -- theorized, unseen particles that neither reflect nor absorb light, but are able to exert gravity -- may comprise 80% of the matter in the universe. Dark matter may explain the very nature of how galaxies form and how the universe is structured. Experiments at Yale and elsewhere are attempting to identify the dark matter particle; the leading candidates include axions and neutralinos. "While we now have a precise cosmic inventory for the amount of dark matter and how it is distributed in the universe, the particle itself remains elusive," Natarajan said. Dark matter particles are thought to provide the unseen mass that is responsible for gravitational lensing, by bending light from distant galaxies. This light bending produces systematic distortions in the shapes of galaxies viewed through the lens. Natarajan's group decoded the distortions to create the new dark matter map. Significantly, the map closely matches computer simulations of dark matter theoretically predicted by the cold dark matter model; cold dark matter moves slowly compared to the speed of light, while hot dark matter moves faster. This agreement with the standard model is notable given that all of the evidence for dark matter thus far is indirect, said the researchers. The high-resolution simulations used in the study, known as the Illustris suite, mimic structure formation in the universe in the context of current accepted theory. A study detailing the findings appeared Feb. 28 in the journal Monthly Notices of the Royal Astronomical Society. Other Yale researchers involved in the study were graduate students Urmila Chadayammuri and Fangzhou Jiang, faculty member Frank van den Bosch, and former postdoctoral fellow Hakim Atek. Additional co-authors came from institutions worldwide: Mathilde Jauzac from the United Kingdom and South Africa; Johan Richard, Eric Jullo, and Marceau Limousin from France; Jean-Paul Kneib from Switzerland; Massimo Meneghetti from Italy; and Illustris simulators Annalisa Pillepich, Ana Coppa, Lars Hernquist, and Mark Vogelsberger from the United States. The research was supported in part by grants from the National Science Foundation, the Science and Technology Facilities Council, and NASA via the Space Telescope Institute HST Frontier Fields initiative.

Rantakyro F.T.,Gemini Observatory | Cardwell A.,Gemini Observatory | Chilcote J.,University of California at Los Angeles | Dunn J.,National Research Council Canada | And 17 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The Gemini Planet Imager is an extreme AO instrument with an integral field spectrograph (IFS) operating in Y, J, H, and K bands. Both the Gemini telescope and the GPI instrument are very complex systems. Our goal is that the combined telescope and instrument system may be run by one observer operating the instrument, and one operator controlling the telescope and the acquisition of light to the instrument. This requires a smooth integration between the two systems and easily operated control interfaces. We discuss the definition of the software and hardware interfaces, their implementation and testing, and the integration of the instrument with the telescope environment. © 2014 SPIE.

Espaillat C.,Harvard - Smithsonian Center for Astrophysics | Furlan E.,Jet Propulsion Laboratory | D'Alessio P.,National Autonomous University of Mexico | Sargent B.,Space Telescope Institute | And 4 more authors.
Astrophysical Journal | Year: 2011

We present a Spitzer IRS study of variability in 14 T Tauri stars in the Taurus and Chamaeleon star-forming regions. The sample is composed of transitional and pre-transitional objects which contain holes and gaps in their disks. We detect variability between 5 and 38 μm in all but two of our objects on timescales of 2-3 years. Most of the variability observed can be classified as seesaw behavior, whereby the emission at shorter wavelengths varies inversely with the emission at longer wavelengths. For many of the objects we can reasonably reproduce the observed variability using irradiated disk models, particularly by changing the height of the inner disk wall by ∼20%. When the inner wall is taller, the emission at the shorter wavelengths is higher since the inner wall dominates the emission at 2-8 μm. The taller inner wall casts a larger shadow on the outer disk wall, leading to less emission at wavelengths beyond 20 μm where the outer wall dominates. We discuss how the possible presence of planets in these disks could lead to warps that cause changes in the height of the inner wall. We also find that crystalline silicates are common in the outer disks of our objects and that in the four disks in the sample with the most crystalline silicates, variability on timescales of 1 week is present. In addition to explaining the infrared variability described above, planets can create shocks and collisions which can crystallize the dust and lead to short timescale variability. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.

Espaillat C.,Harvard - Smithsonian Center for Astrophysics | Ingleby L.,University of Michigan | Furlan E.,National Optical Astronomy Observatory | Furlan E.,Infrared Processing and Analysis Center | And 8 more authors.
Astrophysical Journal | Year: 2013

High-energy radiation from T Tauri stars (TTS) influences the amount and longevity of gas in disks, thereby playing a crucial role in the creation of gas giant planets. Here we probe the high-energy ionizing radiation from TTS using high-resolution mid-infrared (MIR) Spitzer Infrared Spectrograph neon forbidden line detections in a sample of disks from IC 348, NGC 2068, and Chamaeleon. We report three new detections of [Ne III] from CS Cha, SZ Cha, and T 54, doubling the known number of [Ne III] detections from TTS. Using [Ne III]-to-[Ne II] ratios in conjunction with X-ray emission measurements, we probe high-energy radiation from TTS. The majority of previously inferred [Ne III]/[Ne II] ratios based on [Ne III] line upper limits are significantly less than 1, pointing to the dominance of either X-ray radiation or soft extreme-ultraviolet (EUV) radiation in producing these lines. Here we report the first observational evidence for hard EUV-dominated Ne forbidden line production in a T Tauri disk: [Ne III]/[Ne II] ∼ 1 in SZ Cha. Our results provide a unique insight into the EUV emission from TTS, by suggesting that EUV radiation may dominate the creation of Ne forbidden lines, albeit in a minority of cases. © 2013. The American Astronomical Society. All rights reserved.

Ribeiro V.A.R.M.,University of Cape Town | Bode M.F.,Liverpool John Moores University | Williams R.,Space Telescope Institute
Proceedings of the International Astronomical Union | Year: 2012

The nebular remnant of RS Ophiuchi was modelled using combined HST/ACS imaging and ground-based spectroscopy on day 155 after outburst as a two component bipolar expansion with a low velocity innermost hour-glass over density and a more extended high velocity dumbbell structure. The model was evolved to a much later date, day 455 after outburst, when second epoch HST images were secured. However, due to the lack of simultaneous ground-based spectroscopy the evolved model was much harder to constrain. One suggestion put forward was that the dumbbell structure expanded linearly while the inner hour-glass showed signs of deceleration. Archival data in the form of ground-based spectroscopy on day 415 were subsequently obtained. These new data suggest indeed that a non-linear expansion of the system occurred. © International Astronomical Union 2013.

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