Browsing by Subject "radiative transfer"

Now showing 1 - 20 of 24

The Abundances Of Neutron-Capture Species In The Very Metal-Poor Globular Cluster M15: A Uniform Analysis Of Red Giant Branch And Red Horizontal Branch Stars
(2011-06) Sobeck, Jennifer S.; Kraft, Robert P.; Sneden, Christopher; Preston, George W.; Cowan, John J.; Smith, Graeme H.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.; Sneden, Christopher
The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Delta(RHB-RGB) approximate to 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.
Assembly Of The First Disk Galaxies Under Radiative Feedback From Pop III Stars
(2012-05) Pawlik, A. H.; Milosavljevic, M.; Bromm, V.; Pawlik, Andreas H; Milosavljević, Miloš; Bromm, Volker
We investigate how radiative feedback from the first stars affects the assembly of the first dwarf galaxies. We perform cosmological zoomed smoothed particle hydrodynamics simulations of a galaxy assembling inside a halo reaching a virial mass similar to 10(9) M-circle dot at z = 10. The simulations follow the non-equilibrium chemistry and cooling of primordial gas and the subsequent conversion of the cool dense gas into massive metal-free stars. To quantify the radiative feedback, we compare a simulation in which stars emit both molecular hydrogen dissociating and hydrogen ionizing radiation with a simulation in which stars do not emit radiation but remain dark. Photodissociation and photoionization exert a strong negative feedback on the assembly of the galaxy inside the minihalo progenitor, impeding gas condensation and suppressing star formation. The radiative feedback on the gas implies a suppression of the central dark matter densities in the minihalo by factors of up to a few, which is a significant deviation from the singular isothermal density profile characterizing the dark matter distribution in the absence of radiative feedback. The properties of the galaxy become insensitive to the inclusion of radiation once the minihalo turns into an atomic cooler. The formation of a rotationally supported extended disk inside the atomically cooling galaxy therefore is a robust outcome of our simulations. Our simulations make predictions for observations with the upcoming James Webb Space Telescope.
B2 0902+34: A Collapsing Protogiant Elliptical Galaxy At Z=3.4
(2009-03) Adams, Joshua J.; Hill, Gary J.; MacQueen, Phillip J.; Adams, Joshua J.; Hill, Gary J.; MacQueen, Phillip J.
We have used the visible integral-field replicable unit spectrograph prototype, a new integral field spectrograph, to study the spatially and spectrally resolved Lyman-alpha emission line structure in the radio galaxy B2 0902+34 at z = 3.4. We observe a halo of Lyman-alpha emission with a velocity dispersion of approximate to 250 km s(-1) extending to a radius of 50 kpc. A second feature is revealed in a spatially resolved region where the line profile shows blueshifted structure. This may be viewed as either H I absorption at approximate to-450 km s(-1) or secondary emission at approximate to-900 km s(-1) from the primary peak. B2 0902+34 is also the only high-redshift radio galaxy with a detection of 21 cm absorption. Our new data, in combination with the 21 cm absorption, suggest two important and unexplained discrepancies. First, nowhere in the line profiles of the Lyman-alpha halo is the 21 cm absorber population evident. Second, the 21 cm absorption redshift is higher than the Lyman-alpha emission redshift. In an effort to explain these two traits, we have undertaken the first three-dimensional Monte Carlo simulations of resonant scattering in radio galaxies. We have created a simple model with two photoionized cones embedded in a halo of neutral hydrogen. Lyman-alpha photons propagate from these cones through the optically thick H I halo until reaching the virial radius. Though simple, the model produces the features in the Lyman-alpha data and predicts the 21 cm properties. To reach agreement between this model and the data, global infall of the H I is strictly necessary. The amount of gas necessary to match the model and data is surprisingly high, >= 10(12) M(circle dot), an order of magnitude larger than the stellar mass. The collapsing structure and large gas mass lead us to interpret B2 0902+34 as a protogiant elliptical galaxy. This interpretation is a falsifiable alternative to the presence of extended H I shells ejected through feedback events such as starburst superwinds. An understanding of these gas features and a classification of this system's evolutionary Stategive unique observational evidence of the formation events in massive galaxies.
A Candidate Detection of the First Hydrostatic Core
(2010-10) Enoch, Melissa L.; Lee, Jeong-Eun; Harvey, Paul; Dunham, Michael M.; Schnee, Scott; Harvey, Paul; Dunham, Michael M.
The first hydrostatic core (FHSC) represents a very early phase in the low-mass star Formation process, after collapse of the parent core has begun but before a true protostar has formed. This large (few AU), cool (100 K), pressure-supported core of molecular hydrogen is expected from theory, but has yet to be observationally verified. Here, we present observations of an excellent candidate for the FHSC phase: Per-Bolo 58, a dense core in Perseus that was previously believed to be starless. The 70 mu m flux of 65 mJy, from new deep Spitzer MIPS observations, is consistent with that expected for the FHSC. A low signal-to-noise detection at 24 mu m leaves open the possibility that Per-Bolo 58 could be a very low luminosity protostar, however. We utilize radiative transfer models to determine the best-fitting FHSC and protostar models to the spectral energy distribution and 2.9 mm visibilities of Per-Bolo 58. The source is consistent with an FHSC with some source of lower opacity through the envelope allowing 24 mu m emission to escape; a small outflow cavity and a cavity in the envelope are both possible. While we are unable to rule out the presence of a protostar, if present it would be one of the lowest luminosity protostellar objects yet observed, with an internal luminosity of similar to 0.01 L(circle dot).
Center-To-Limb Variation Of Solar Three-Dimensional Hydrodynamical Simulations
(2008-06) Koesterke, Lars; Prieto, Carlos Allende; Lambert, David L.; Koesterke, Lars; Prieto, Carlos Allende; Lambert, David L.
We examine closely the solar center-to-limb variation of continua and lines and compare observations with predictions from both a three-dimensional (3D) hydrodynamic simulation of the solar surface ( provided by M. Asplund and collaborators) and one-dimensional (1D) model atmospheres. Intensities from the 3D time series are derived by means of the new synthesis code ASS epsilon T, which overcomes limitations of previously available codes by including a consistent treatment of scattering and allowing for arbitrarily complex line and continuum opacities. In the continuum, we find very similar discrepancies between synthesis and observation for both types of model atmospheres. This is in contrast to previous studies that used a "horizontal'' and time-averaged representation of the 3D model and found a significantly larger disagreement with observations. The presence of temperature and velocity fields in the 3D simulation provides a significant advantage when it comes to reproducing solar spectral line shapes. Nonetheless, a comparison of observed and synthetic equivalent widths reveals that the 3D model also predicts more uniform abundances as a function of position angle on the disk. We conclude that the 3D simulation provides not only a more realistic description of the gas dynamics, but despite its simplified treatment of the radiation transport, it also predicts reasonably well the observed center-to-limb variation, which is indicative of a thermal structure free from significant systematic errors.
Cosmological Impact Of Population III Binaries
(2015-03) Chen, Ke-Jung; Bromm, Volker; Heger, Alexander; Jeon, Myoungwon; Woosley, Stan; Chen, Ke-Jung; Woosley, Stan
We present the results of the stellar feedback from Population III (Pop III) binaries by employing improved, more realistic Pop III evolutionary stellar models. To facilitate a meaningful comparison, we consider a fixed mass of 60 M-circle dot incorporated in Pop III stars, either contained in a single star, or split up in binary stars of 30 M-circle dot each or an asymmetric case of one 45 and one 15 M-circle dot star. Whereas the sizes of the resulting H II regions are comparable across all cases, the He III regions around binary stars are significantly smaller than that of the single star. Consequently, the He+ 1640 angstrom recombination line is expected to become much weaker. Supernova (SN) feedback exhibits great variety due to the uncertainty in possible explosion pathways. If at least one of the component stars dies as a hypernova about 10 times more energetic than conventional core-collapse SNe, the gas inside the host minihalo is effectively blown out, chemically enriching the intergalactic medium (IGM) to an average metallicity of 10(-4)-10(-3) Z(circle dot), out to similar to 2 kpc. The single star, however, is more likely to collapse into a black hole, accompanied by at most very weak explosions. The effectiveness of early chemical enrichment would thus be significantly reduced, in contrast to. the lower mass binary stars, where at least one component is likely to contribute to heavy element production and dispersal. Important new feedback physics is also introduced if close binaries can form high-mass X-ray binaries, leading to the pre-heating and -ionization of the IGM beyond the extent of the stellar H II regions.
Detecting the Rise and Fall of the First Stars by Their Impact on Cosmic Reionization
(2012-09) Ahn, Kyungjin; Iliev, Ilian T.; Shapiro, Paul R.; Mellema, Garrelt; Koda, Jun; Mao, Yi; Shapiro, Paul R.; Mao, Yi
The intergalactic medium was reionized before redshift z similar to 6, most likely by starlight which escaped from early galaxies. The very first stars formed when hydrogen molecules (H-2) cooled gas inside the smallest galaxies, minihalos (MHs) of mass between 10(5) and 10(8) M-circle dot. Although the very first stars began forming inside these MHs before redshift z similar to 40, their contribution has, to date, been ignored in large-scale simulations of this cosmic reionization. Here we report results from the first reionization simulations to include these first stars and the radiative feedback that limited their Formation, in a volume large enough to follow the crucial spatial variations that influenced the process and its observability. We show that, while MH stars stopped far short of fully ionizing the universe, reionization began much earlier with MH sources than without, and was greatly extended, which boosts the intergalactic electron-scattering optical depth and the large-angle polarization fluctuations of the cosmic microwave background significantly. This boost should be readily detectable by Planck, although within current Wilkinson Microwave Anisotropy Probe uncertainties. If reionization ended as late as z(ov) less than or similar to 7, as suggested by other observations, Planck will thereby see the signature of the first stars at high redshift, currently undetectable by other probes.
Dust, Ice, and Gas in Time (DIGIT) Herschel Observations of GSS30-IRS1 in Ophiuchus
(2015-03) Je, Hyerin; Lee, Jeong-Eun; Lee, Seokho; Green, Joel D.; Evans, Neal J., II; ee, Jeong-Eun; Green, Joel D.; Evans, Neal J., II
As a part of the "Dust, Ice, and Gas In Time" (DIGIT) key program on Herschel, we observed GSS30-IRS1, a Class I protostar located in Ophiuchus (d = 120 pc), with Herschel/Photodetector Array Camera and Spectrometer. More than 70 lines were detected within a wavelength range from 50 to 200 mu m, including CO, H2O, OH, and two atomic [O I] lines at 63 and 145 mu m. The [C II] line, known as a tracer of externally heated gas by the interstellar radiation field (ISRF), is also detected at 158 mu m. All lines, except [O I] and [C II], are detected only at the central spaxel of 9 ''.4 x 9 ''.4. The [O I] emissions are extended along a NE-SW orientation, and the [C II] line is detected over all spaxels, indicative of an external photodissociation region. The total [C II] intensity around GSS30 reveals that the far-ultraviolet radiation field is in the range of 3 to 20 G(0), where G(0) is in units of the Habing Field, 1.6 x 10(-3) erg cm(-2) s(-1). This enhanced external radiation field heats the envelope of GSS30-IRS1, causing the continuum emission to be extended, unlike the molecular emission. The best-fit continuum model of GSS30-IRS1 with the physical structure including flared disk, envelope, and outflow shows that the internal luminosity is 10 L-circle dot, and the region is externally heated by a radiation field enhanced by a factor of 130 compared to the standard local ISRF.
Emission From Pair-Instability Supernovae With Rotation
(2015-01) Chatzopoulos, Emmanouil; van Rossum, Daniel R.; Wheeler, Craig J.; Whalen, Daniel J.; Smidt, Joseph; Wiggins, Brandon; Wheeler, Craig J.
Pair-instability supernovae (PISNe) have been suggested as candidates for some superluminous supernovae, such as SN 2007bi, and as one of the dominant types of explosion occurring in the early universe from massive, zero-metallicity Population III stars. The progenitors of such events can be rapidly rotating, therefore exhibiting different evolutionary properties due to the effects of rotationally induced mixing and mass-loss. Proper identification of such events requires rigorous radiation hydrodynamics and radiative transfer calculations that capture not only the behavior of the light curve but also the spectral evolution of these events. We present radiation hydrodynamics and radiation transport calculations for 90-300M(circle dot) rotating PISNe covering both the shock breakout and late light curve phases. We also investigate cases of different initial metallicity and rotation rate to determine the impact of these parameters on the detailed spectral characteristics of these events. In agreement with recent results on non-rotating PISNe, we find that for a range of progenitor masses and rotation rates these events have intrinsically red colors in contradiction with observations of superluminous supernovae. The spectroscopic properties of rotating PISNe are similar to those of non-rotating events with stripped hydrogen and helium envelopes. We find that the progenitor metallicity and rotation rate properties are erased after the explosion and cannot be identified in the resulting model spectra. It is the combined effects of pre-supernova mass-loss and the basic properties of the supernova ejecta such as mass, temperature, and velocity that have the most direct impact in the model spectra of PISNe.
The First Galaxies: Assembly Under Radiative Feedback From The First Stars
(2013-04) Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker
We investigate how radiative feedback from the first stars affects the assembly of the first dwarf galaxies. To this end, we perform cosmological zoomed smoothed particle hydrodynamics simulations of a dwarf galaxy assembling inside a halo reaching a virial mass similar to 10(9) M-circle dot at z = 10. The simulations follow the non-equilibrium chemistry and cooling of primordial gas and the subsequent conversion of the cool dense gas into massive metal-free stars. To quantify the radiative feedback, we compare a simulation in which stars emit both molecular hydrogen dissociating and hydrogen/helium ionizing radiation with a simulation in which stars emit only molecular hydrogen dissociating radiation, and further with a simulation in which stars remain dark. Photodissociation and photoionization exert a strong negative feedback on the assembly of the galaxy inside the main minihalo progenitor. Gas condensation is strongly impeded, and star formation is strongly suppressed in comparison with the simulation in which stars remain dark. The feedback on the gas from either dissociating or ionizing radiation implies a suppression of the central dark matter densities in the minihalo progenitor by factors of up to a few, which is a significant deviation from the singular isothermal density profile characterizing the dark matter distribution inside the virial radius in the absence of radiative feedback. The evolution of gas densities, star formation rates, and the distribution of dark matter becomes insensitive to the inclusion of dissociating radiation in the late stages of the minihalo assembly, and it becomes insensitive to the inclusion of ionizing radiation once the minihalo turns into an atomically cooling galaxy. The formation of a rotationally supported extended disk inside the dwarf galaxy is a robust outcome of our simulations not affected by the inclusion of radiation. Low-mass galaxies in the neighborhood of the dwarf galaxy show a large scatter in the baryon fraction which is driven by radiative feedback from sources both internal and external to these galaxies. Our estimates of the observability of the first galaxies show that dwarf galaxies such as simulated here will be among the faintest galaxies the upcoming James Webb Space Telescope will detect. Our conclusions regarding the structure and observability of the first galaxies are subject to our neglect of feedback from supernovae and chemical enrichment as well as to statistical uncertainties implied by the limited number of galaxies in our simulations.
Herschel Images Of Fomalhaut An Extrasolar Kuiper Belt At The Height Of Its Dynamical Activity
(2012-04) Acke, B.; Min, M.; Dominik, C.; Vandenbussche, B.; Sibthorpe, B.; Waelkens, C.; Olofsson, G.; Degroote, P.; Smolders, K.; Pantin, E.; Barlow, M. J.; Blommaert, Jadl; Brandeker, A.; De Meester, W.; Dent, W. R. F.; Exter, K.; Di Francesco, J.; Fridlund, M.; Gear, W. K.; Glauser, A. M.; Greaves, J. S.; Harvey, P. M.; Henning, T.; Hogerheijde, M. R.; Holland, W. S.; Huygen, R.; Ivison, R. J.; Jean, C.; Liseau, R.; Naylor, D. A.; Pilbratt, G. L.; Polehampton, E. T.; Regibo, S.; Royer, P.; Sicilia-Aguilar, A.; Swinyard, B. M.; Harvey, P. M.
Context. Fomalhaut is a young (2 +/- 1 x 10(8) years), nearby (7.7 pc), 2 M-circle dot star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 '' and 36.7 '' at wavelengths between 70 mu m and 500 mu m. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.
The Inhomogeneous Background Of H-2-Dissociating Radiation During Cosmic Reionization
(2009-04) Ahn, Kyungjin; Shapiro, Paul R.; Iliev, Illian T.; Mellema, Garrelt; Pen, Ue-Li; Shapiro, Paul R.
The first, self-consistent calculations are presented of the cosmological, H-2-dissociating UV background produced during the epoch of reionization by the sources of reionization. Large-scale radiative transfer simulations of reionization trace the impact of all the ionizing starlight on the intergalactic medium (IGM) from all the sources in our simulation volume down to dwarf galaxies of mass similar to 10(8) M-circle dot, identified by very high resolution N-body simulations, including the self-regulating effect of IGM photoheating on dwarf galaxy formation. The UV continuum emitted below 13.6 eV by each source is then transferred through the same IGM, attenuated by atomic H Lyman series resonance lines, to predict the evolution of the inhomogeneous radiation background in the Lyman-Werner (LW) bands of H-2 between 11 and 13.6 eV. On average, the intensity of this LW background is found to rise to the threshold level at which dissociation suppresses H-2 cooling and star formation inside minihalos, long before reionization is complete. Spatial variations in the LW background are found which result from the clustering of sources associated with large-scale structure formation, such that intensity fluctuations correlate with matter density fluctuations. As a result, the LW background rises to the threshold level for H-2 suppression earlier in the vicinity of the reionization sources and their H II regions.
Interpretation Of Infrared Vibration-Rotation Spectra Of Interstellar And Circumstellar Molecules
(2013-03) Lacy, John H.; Lacy, John H.
Infrared vibration-rotation lines can be valuable probes of interstellar and circumstellar molecules, especially symmetric molecules, which have no pure rotational transitions. But most such observations have been interpreted with an isothermal absorbing slab model, which leaves out important radiative transfer and molecular excitation effects. A more realistic non-LTE and non-isothermal radiative transfer model has been constructed. The results of this model are in much better agreement with the observations, including cases where lines in one branch of a vibration-rotation band are in absorption and another in emission. In general, conclusions based on the isothermal absorbing slab model can be very misleading, but the assumption of LTE may not lead to such large errors, particularly if the radiation field temperature is close to the gas temperature.
The Kinetic Sunyaev-Zel'Dovich Effect As A Probe Of The Physics Of Cosmic Reionization: The Effect Of Self-Regulated Reionization
(2013-06) Park, Hyunbae; Shapiro, Paul R.; Komatsu, Eiichiro; Iliev, Illian T.; Ahn, Kyungjin; Mellema, Garrelt; Park, Hyunbae; Shapiro, Paul R.; Komatsu, Eiichiro
We calculate the angular power spectrum of the cosmic microwave background temperature fluctuations induced by the kinetic Sunyaev-Zel'dovich (kSZ) effect from the epoch of reionization (EOR). We use detailed N-body+radiative-transfer simulations to follow inhomogeneous reionization of the intergalactic medium. For the first time, we take into account the "self-regulation" of reionization: star formation in low-mass dwarf galaxies (10(8) M-circle dot less than or similar to M less than or similar to 10(9) M-circle dot) or minihalos (10(5) M-circle dot less than or similar to M less than or similar to 10(8) M-circle dot) is suppressed if these halos form in the regions that were already ionized or Lyman-Werner dissociated. Some previous work suggested that the amplitude of the kSZ power spectrum from the EOR can be described by a two-parameter family: the epoch of half-ionization and the duration of reionization. However, we argue that this picture applies only to simple forms of the reionization history which are roughly symmetric about the half-ionization epoch. In self-regulated reionization, the universe begins to be ionized early, maintains a low level of ionization for an extended period, and then finishes reionization as soon as high-mass atomically cooling halos dominate. While inclusion of self-regulation affects the amplitude of the kSZ power spectrum only modestly (similar to 10%), it can change the duration of reionization by a factor of more than two. We conclude that the simple two-parameter family does not capture the effect of a physical, yet complex, reionization history caused by self-regulation. When added to the post-reionization kSZ contribution, our prediction for the total kSZ power spectrum is below the current upper bound from the South Pole Telescope. Therefore, the current upper bound on the kSZ effect from the EOR is consistent with our understanding of the physics of reionization.
Low Abundance, Strong Features: Window-Dressing Crystalline Forsterite In The Disk Wall Of HD 100546
(2011-07) Mulders, G. D.; Waters, Lbfm; Dominik, C.; Sturm, B.; Bouwman, J.; Min, M.; Verhoeff, A. P.; Acke, B.; Augereau, J. C.; Evans, Neal J.; Henning, T.; Meeus, G.; Olofsson, J.; Evans, Neal J.
Context. Forsterite is one of the crystalline dust species that is often observed in protoplanetary disks and solar system comets. Being absent in the interstellar medium, it must be produced during the disk lifetime. It can therefore serve as a tracer of dust processing and disk evolution, which can lead to a better understanding of the physical processes occurring in the disk, and possibly planet formation. However, the connection of these processes with the overall disk crystallinity remains unclear. Aims. We aim to characterize the forsterite abundance and spatial distribution in the disk of the Herbig Be star HD 100546, to investigate if a connection exists with the large disk gap. Methods. We use a 2D radiative transfer code, MCMax, to model the circumstellar dust around HD 100546. We use VISIR Q-band imaging to probe the outer disk geometry and mid-infrared features to model the spatial distribution of forsterite. The temperature-dependent shape of the 69 mu m feature observed with Herschel***/PACS is used as a critical tool to constrain this distribution. Results. We find a crystalline mass fraction of 40-60%, located close to the disk wall between 13 and 20 AU, and possibly farther out at the disk surface. The forsterite is in thermal contact with the other dust species. We put an upper limit on the iron content of forsterite of 0.3%. Conclusions. Optical depth effects play a key role in explaining the observed forsterite features, hiding warm forsterite from view at short wavelengths. The disk wall acts as a showcase: it displays a localized high abundance of forsterite, which gives rise to a high observed crystallinity, while the overall mass fraction of forsterite is a factor of ten lower.
Near-Infrared Line Identification In Type Ia Supernovae During The Transitional Phase
(2014-09) Friesen, Brian; Baron, E.; Wisniewski, John P.; Parrent, Jerod T.; Thomas, R. C.; Miller, Timothy R.; Marion, G. H.; Marion, G. H.
We present near-infrared synthetic spectra of a delayed-detonation hydrodynamical model and compare them to observed spectra of four normal Type Ia supernovae ranging from day +56.5 to day +85. This is the epoch during which supernovae are believed to be undergoing the transition from the photospheric phase, where spectra are characterized by line scattering above an optically thick photosphere, to the nebular phase, where spectra consist of optically thin emission from forbidden lines. We find that most spectral features in the near-infrared can be accounted for by permitted lines of Fe II and Co II. In addition, we find that [Ni II] fits the emission feature near 1.98 mu m, suggesting that a substantial mass of Ni-58 exists near the center of the ejecta in these objects, arising from nuclear burning at high density.
New ATLAS9 And MARCS Model Atmosphere Grids For The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
(2012-10) Meszaros, Sz.; Prieto, C. Allende; Edvardsson, B.; Castelli, F.; Perez, A. E. G.; Gustafsson, B.; Majewski, S. R.; Plez, B.; Schiavon, R.; Shetrone, M.; de Vicente, A.; Shetrone, Matthew D.
We present a new grid of model photospheres for the SDSS-III/APOGEE survey of stellar populations of the Galaxy, calculated using the ATLAS9 and MARCS codes. New opacity distribution functions were generated to calculate ATLAS9 model photospheres. MARCS models were calculated based on opacity sampling techniques. The metallicity ([M/H]) spans from -5 to 1.5 for ATLAS and -2.5 to 0.5 for MARCS models. There are three main differences with respect to previous ATLAS9 model grids: a new corrected H2O line list, a wide range of carbon ([C/M]) and alpha element [alpha/M] variations, and solar reference abundances from Asplund et al. The added range of varying carbon and alpha-element abundances also extends the previously calculated MARCS model grids. Altogether, 1980 chemical compositions were used for the ATLAS9 grid and 175 for the MARCS grid. Over 808,000 ATLAS9 models were computed spanning temperatures from 3500 K to 30,000 K and log g from 0 to 5, where larger temperatures only have high gravities. The MARCS models span from 3500 K to 5500 K, and log g from 0 to 5. All model atmospheres are publicly available online.
New ATLAS9 And MARCS Model Atmosphere Grids For The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
(2012-10) Meszaros, Sz.; Prieto, C. Allende; Edvardsson, B.; Castelli, F.; Perez, A. E. G.; Gustafsson, B.; Majewski, S. R.; Plez, B.; Schiavon, R.; Shetrone, M.; de Vicente, A.; Shetrone, Matthew D.
We present a new grid of model photospheres for the SDSS-III/APOGEE survey of stellar populations of the Galaxy, calculated using the ATLAS9 and MARCS codes. New opacity distribution functions were generated to calculate ATLAS9 model photospheres. MARCS models were calculated based on opacity sampling techniques. The metallicity ([M/H]) spans from -5 to 1.5 for ATLAS and -2.5 to 0.5 for MARCS models. There are three main differences with respect to previous ATLAS9 model grids: a new corrected H2O line list, a wide range of carbon ([C/M]) and alpha element [alpha/M] variations, and solar reference abundances from Asplund et al. The added range of varying carbon and alpha-element abundances also extends the previously calculated MARCS model grids. Altogether, 1980 chemical compositions were used for the ATLAS9 grid and 175 for the MARCS grid. Over 808,000 ATLAS9 models were computed spanning temperatures from 3500 K to 30,000 K and log g from 0 to 5, where larger temperatures only have high gravities. The MARCS models span from 3500 K to 5500 K, and log g from 0 to 5. All model atmospheres are publicly available online.
New H-Band Stellar Spectral Libraries For The SDSS-III/APOGEE Survey
(2015-06) Zamora, O.; Garcia-Hernandez, D. A.; Prieto, C. A.; Carrera, R.; Koesterke, L.; Edvardsson, B.; Castelli, F.; Plez, B.; Bizyaev, D.; Cunha, K.; Perez, A. E. G.; Gustafsson, B.; Holtzman, J. A.; Lawler, J. E.; Majewski, S. R.; Manchado, A.; Meszaros, S.; Shane, N.; Shetrone, M.; Smith, V. V.; Zasowski, G.; Koesterke, L.
The Sloan Digital Sky Survey-III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) has obtained high-resolution (R similar to 22,500), high signal-to-noise ratio (>100) spectra in the H-band (similar to 1.5-1.7 mu m) for about 146,000 stars in the Milky Way galaxy. We have computed spectral libraries with effective temperature (T-eff) ranging from 3500 to 8000 K for the automated chemical analysis of the survey data. The libraries, used to derive stellar parameters and abundances from the APOGEE spectra in the SDSS-III data release 12 (DR12), are based on ATLAS9 model atmospheres and the ASS epsilon T spectral synthesis code. We present a second set of libraries based on MARCS model atmospheres and the spectral synthesis code Turbospectrum. The ATLAS9/ASS epsilon T (T-eff = 3500-8000 K) and MARCS/Turbospectrum (T-eff = 3500-5500 K) grids cover a wide range of metallicity (-2.5 <= [M/H] <= + 0.5 dex), surface gravity (0 <= log g <= 5 dex), microturbulence (0.5 <= xi <= 8 km s(-1)), carbon (-1 <= [C/M] <= + 1 dex), nitrogen (-1 <= [N/M] <= + 1 dex), and alpha-element (-1 <= [alpha/M] <= + 1 dex) variations, having thus seven dimensions. We compare the ATLAS9/ASS.T and MARCS/Turbospectrum libraries and apply both of them to the analysis of the observed H-band spectra of the Sun and the K2 giant Arcturus, as well as to a selected sample of well-known giant stars observed at very high resolution. The new APOGEE libraries are publicly available and can be employed for chemical studies in the H-band using other high-resolution spectrographs.
Non-Detection Of L-Band Line Emission From The Exoplanet HD189733B
(2011-02) Mandell, Avi M.; Deming, L. Drake; Blake, Geoffrey A.; Knutson, Heather A.; Mumma, Michael J.; Villanueva, Geronimo L.; Salyk, Colette; Salyk, Colette
We attempt to confirm bright non-local thermodynamic equilibrium (non-LTE) emission from the exoplanet HD 189733b at 3.25 mu m, as recently reported by Swain et al. based on observations at low spectral resolving power (lambda/delta lambda approximate to 30). Non-LTE emission lines from gas in an exoplanet atmosphere will not be significantly broadened by collisions, so the measured emission intensity per resolution element must be substantially brighter when observed at high spectral resolving power. We observed the planet before, during, and after a secondary eclipse event at a resolving power lambda/delta lambda = 27, 000 using the NIRSPEC spectrometer on the Keck II telescope. Our spectra cover a spectral window near the peak found by Swain et al., and we compare emission cases that could account for the magnitude and wavelength dependence of the Swain et al. result with our final spectral residuals. To model the expected line emission, we use a general non-equilibrium formulation to synthesize emission features from all plausible molecules that emit in this spectral region. In every case, we detect no line emission to a high degree of confidence. After considering possible explanations for the Swain et al. results and the disparity with our own data, we conclude that an astrophysical source for the putative non-LTE emission is unlikely. We note that the wavelength dependence of the signal seen by Swain et al. closely matches the 2 nu(2) band of water vapor at 300 K, and we suggest that an imperfect correction for telluric water is the source of the feature claimed by Swain et al.