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Before TES (Thermal Emission Spectrometry) spectra can be used to model surface compositions, they must have a strong atmospheric compensation applied. We explore a very different atmospheric retrieval process, and compare results and implications for the derived surface composition. Additional information is contained in the original extended abstract.
The Thermal Emission Spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase, together with about a 35 percent dust component provides the best fit to the spectrum. Qualitative upper limits can be placed on the concentration of carbonates (<10 percent), olivine (<10 percent), clay minerals (<20 percent), and quartz (<5 percent) in the limited regions observed. Limb observations in the northern hemisphere reveal low-lying dust hazes and detached water-ice clouds at altitudes up to 55 kilometers. At an aerocentric longitude of 224 degrees a major dust storm developed in the Noachis Terra region. The south polar cap retreat was similar to that observed by Viking.
Gamma-ray bursts are the largest explosions in the Universe. The radiation is thought to come from a hypernova initiated from the collapse of a massive star or perhaps the merger of two compact stars such s neutron stars and/or black holes. Most of the observed energy is radiated as gamma rays, usually lasting from a fraction of a second to several hundred seconds. The energy generation process is usually referred to as the "central engine". Observed properties of this prompt emission, including spectra, time profiles and durations will be discussed. The history of these observations and future GRB spacecraft will also be described.
We present new emission line spectra and an analysis of the mass outflow for the massive binary, HD 149404.
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The spectral shapes of the contributions of different classes of unresolved gamma-ray emitters can provide insight into their relative contributions to the extragalactic gamma-ray background (EGB) and the natures of their spectra at GeV energies, We calculate the spectral shapes of the contributions to the EGB arising from BL Lacertae type objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) assuming blazar spectra can be described as broken power laws, We fit the resulting total blazar spectral shape to the Fermi Large Area Telescope measurements of the EGB, finding that the best-fit shape reproduces well the shape of the Fermi EGB for various break scenarios. We conclude that a scenario in which the contribution of blazars is dominant cannot be excluded on spectral grounds alone, even if spectral breaks are shown to be common among Fermi blazars. We also find that while the observation of a featureless (within uncertainties) power-law EGB spectrum by Fermi does not necessarily imply a single class of contributing unresolved sources with featureless individual spectra, such an observation and the collective spectra of the separate contributing populations determine the ratios of their contributions. As such, a comparison with studies including blazar gamma-ray luminosity functions could have profound implications for the blazar contribution to the EGB, blazar evolution, and blazar gamma-ray spectra and emission.
This is the second of two papers examining Spitzer Infrared Spectrograph observations of the ultraluminous X-ray source (ULX) in Holmberg II. Here, we perform detailed photoionization modeling of the infrared lines. Our analysis suggests that the luminosity and morphology of the [Oiv] 25.89 micronmeters emission line is consistent with photoionization by the soft X-ray and far ultraviolet (FUV) radiation from the accretion disk of the binary system and inconsistent with narrow beaming. We show that the emission nebula is matter bounded both in the line-of-sight direction and to the east, and probably radiation-bounded to the west. A bolometric luminosity in excess of 10(exp 40) erg s(exp -1) would be needed to produce the measured [O iv] flux. We use modeling and previously published studies to conclude that shocks likely contribute very little, if at all,to the high-ionization line fluxes observed in the Holmberg II ULX. Additionally, we find that the spectral type of the companion star has a surprisingly strong effect on the predicted strength of the [O iv] emission. This finding could explain the origin of [O iv] in some starburst systems containing black hole binaries.
One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.
13 CO and C 18 O observations of HH 1-2 VLA and SSV 63, the exciting stars of the HH 1-2 and HH 24 outflows, have been obtained with the Owens Valley Millimeter Array. The HH 1-2 source has been detected in both lines and in the 2.7 mm continuum. In the continuum, the central source appears unresolved in the 5" beam with a flux density of 20 mJy. A secondary peak of 8 mJy appears 12" SE of VLA 1. A strong peak of molecular line emission appears at the position of VLA 1. Molecular gas associated with SSV 63 has also been detected. Maps of circumstellar material of both sources will be presented.
The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft successfully collected a sample of regolith from asteroid (101955) Bennu on October 20, 2020[1]. The Touch-and-Go (TAG) spacecraft maneuver used to collect the sample mobilized material, including very fine particles (dust),from up to ~1m in depth and ~10m in diameter from the point of contact with the asteroid [1,2].TAG created a dust plume that intercepted the spacecraft and accumulated on the instruments. As a result, all instruments show degradation in optical throughput, with the degree of degradation depending on their aperture size, orientation, and position on the spacecraft [1]. In this study, we analyzed OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) from before and after TAG to assess the dust on the instrument with implications for Bennu’s dust composition and scattering properties, and future visible–near-infrared (VNIR)spectral observations with the OSIRIS-REx spacecraft. OVIRS is a point spectrometer that measures reflected light at VNIR wavelengths from 0.4 to 4.3 μm with a 4 mrad circular field of view(FOV) [3]. Previous observations with OVIRS revealed widespread hydrated minerals and carbon-bearing materials on Bennu [4,5]. A ~3 μm absorption feature is observed globally in OVIRS spectra, with a band position and depth that is consistent with Mg/Fe phyllosilicates and suggests a similar degree of aqueous alteration to that experienced by some carbonaceous chondrite meteorites[4,6]. A series of weak (<5%) VNIR spectral features, potentially associated with hydrated phyllosilicates and iron oxides, are also found in OVIRS spectra (Fig. 1), though not typically observed in meteorite spectra [7]. OSIRIS-REx Thermal Emission Spectrometer (OTES) spectra are consistent with a very thin accumulation (a few to ~ten microns) of fine particles (<~65–100 microns in size)across the surface of Bennu, and particularly on the roughest boulders, an interpretation that is supported by the dust plume seen during TAG [1,8]. An analysis of TAG contamination on the OTES optics revealed a 15% decrease in throughput, and OTES observations of space with and without that contamination allow a recreation of the thermal infrared spectrum [1]. The spectrum of the contamination lacks volume scattering features and exhibits a stronger Mg-OH absorption (~16.5 μm) than average Bennu, suggesting a Mg-rich phyllosilicate composition [1,6]. Here we present the first compositional analysis of Bennu dust at VNIR wavelengths by analyzing the contaminant on OVIRS.
10-micron spectra of many extreme carbon stars reveal a prominent emission feature near 11 microns. This is compared with laboratory spectra of SiC grains. Two distinct types of features are found, perhaps indicative of different mechanisms of grain formation in different stars. Estimates are made of probable column densities and total masses of SiC in the circumstellar shells.
Far-ultraviolet spectra of diffuse emission from a region in the Taurus molecular cloud are presented. These data were obtained with the Berkeley spectrometer on NASA's Ultraviolet Experiment (UVX) payload. The intensity of the continuum emission drops as the optical depth increases toward the denser part of the cloud, an effect which is the opposite of that observed for the diffuse flux at high galactic latitudes. At the center of the aperture, the optical depth is very large, and the continuum emission must be produced by backscattering. At the edges of the cloud, the continuum intensity rises by a factor of 2. The data are interpreted with a new radiative transfer model, which is significantly more sophisticated than its predecessors. If the grain scattering properties are constant across the cloud, a unique best-fit combination can be determined from the data. The best-fit albedo is 0.6 +/- 0.1 at 1600 A. The best-fit value for the phase factor g is 0.5 +/- 0.15. The intensity of the flourescence of H2, combined with an upper limit to the column density of atomic hydrogen associated with the cloud, sets a lower limit of about 130/cm to the density in the flourescence region. Our estimate of the flux incident on the cloud at 1000 A is a factor of 2 to 3 lower than the value required to produce the measured flourescence intensity. Most mechanisms which might reconcile the discrepancy reduce the derived albedo and phase factor.
Spectra of the North Equatorial Belt of Jupiter were obtained in March 1992 at an unapodized resolution of 0.1/cm between 2450 and 2600/cm with the Fourier Transform Spectrometer at the 3.6 m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea. Several emissions from the nu(sub 2) band of H3(+) were detected. The excitation temperature derived from the relative intensities of these emissions averaged over a wide range of longitudes is 800 +/- 100 K, and the H3(+) column density is 1.56(sup +1.0)(sub -0.5) x 10(exp 11)/sq. cm. In addition, several strong absorption features due to (13)CH4 were observed. A comparison between (12)CH4 and (13)CH4 absorptions allowed us to obtain a new measurement of the C-12/C-13 ratio. We found that this ratio, estimated for the first time in this spectral range, is 89 (+/- 25), in agreement with the terrestrial value.
Spectra of 3 microns emission features have been obtained at several positions within the reflection nebulae NGC 1333 SVS3 and NGC 2023. Strong variations of the relative intensities of the 3.29 microns feature and its most prominent satellite band at 3.40 microns are found. It is shown that: (1) the 3.40 microns band is too intense with respect to the 3.29 microns band at certain positions to arise from hot band emission alone, (2) the 3.40 microns band can be reasonably well matched by new laboratory spectra of gas-phase polycyclic aromatic hydrocarbons (PAHs) with alkyl (-CH3) side groups, and (3) the variations in the 3.40 microns to 3.29 microns band intensity ratios are consistent with the photochemical erosion of alkylated PAHs. We conclude that the 3.40 microns emission feature is attributable to -CH3 side groups on PAH molecules. We predict a value of 0.5 for the peak intensity ratio of the 3.40 and 3.29 microns emission bands from free PAHs in the diffuse interstellar medium, which would correspond to a proportion of one methyl group for four peripheral hydrogens. We also compare the 3 microns spectrum of the proto-planetary nebula IRAS 05341 + 0852 with the spectrum of the planetary nebula IRAS 21282 + 5050. We suggest that a photochemical evolution of the initial aliphatic and aromatic hydrocarbon mixture formed in the outflow is responsible for the changes observed in the 3 microns emission spectra of these objects.
Spectra of 3 micrometers emission features have been obtained at several positions within the reflection nebulae NGC 1333 SVS3 and NGC 2023. Strong variations of the relative intensities of the 3.29 micrometers feature and its most prominent satellite band at 3.40 micrometers are found. It is shown that (i) the 3.40 micrometers band is too intense with respect to the 3.29 micrometers band at certain positions to arise from hot band emission alone, (ii) the 3.40 micrometers band can be reasonably well matched by new laboratory spectra of gas-phase polycyclic aromatic hydrocarbons (PAHs) with alkyl (-CH3) side groups, and (iii) the variations in the 3.40 micrometers to 3.29 micrometers band intensity ratios are consistent with the photochemical erosion of alkylated PAHs. We conclude that the 3.40 micrometers emission feature is attributable to -CH3 side groups on PAH molecules. We predict a value of 0.5 for the peak intensity ratio of the 3.40 and 3.29 micrometers emission bands from free PAHs in the diffuse interstellar medium, which would correspond to a proportion of one methyl group for four peripheral hydrogens. We also compare the 3 micrometers spectrum of the proto-planetary nebula IRAS 05341+0852 with the spectrum of the planetary nebula IRAS 21282+5050. We suggest that a photochemical evolution of the initial aliphatic and aromatic hydrocarbon mixture formed in the outflow is responsible for the changes observed in the 3 micrometers emission spectra of these objects.
Faint, diffuse emissions near 1380 A in deeply exposed IUE spectrograms of the red giant Arcturus very likely are associated with bands of the A-X fourth-positive system of carbon monoxide, fluoresced by multiplet UV2 of neutral oxygen near 1305 A. Numerical simulations indicate that the strength of the CO bands is exceedingly sensitive, in the best available one-dimensional model of the chromosphere of Arcturus, to a delicate balance between the rapid inward attenuation of the oxygen radiation field and the rapid outward decline of the molecular absorptivity. The fortuitous character of the overlap region in the single-component model argues that one should also consider the possibility that the pumping occurs in a highly inhomogeneous chromosphere, of the type proposed in previous studies of Arcturus based on observations of the infrared absorption bands of CO.
We report on a series of X-ray spectra of the supermassive star Eta Carinae obtained by the High Energy Transmission Grating Spectrometer on the CHANDRA X-ray observatory before, during and after the star's X-ray minimum in the summer of 2003. The X-ray spectra show significant variations in emission measure and absorption, in the strength of the iron K edge and fluorescent iron emission, but show little change in the distribution of emission measure with temperature. The CHANDRA spectra also resolve emission from Si, S, Fe and other elements in H-like and He-like configurations. The HETGS spectra show that these lines change in centroid energy along with evidence of changes in the forbidden-to-intercombination ratios of the He-like triplets. These spectra offer strong support that the X-ray emission originates within a shock cone around an unseen, massive companion. The variations of the X-ray line spectrum provide a direct measure of the dynamics of the shocked gas in this cone and also evidence that the hottest region of the shock is not always in collisional ionization equilibrium. We discuss these results in light of the recent discovery of He II 4686 emission and the reported discovery of FUV emission from the companion star. This work was supported by SAO/Chandra grant GO3-4008A.
Results of a Roengten Satellite (ROSAT) X-ray survey of 12 nearby near-main-sequence B stars are presented. Objects with very low interstellar hydrogen column density were chosen to study the soft X-ray emission properties of the stars. All of the stars were detected at the 3 sigma level. Spectral fits to seven of the stars are presented, and temperatures and source emission measures are derived. The spectra and characterized by emission from gas at a temperature of about 2 x 10(exp 6) K, which is lower than that typically observed for O stars. The ratio L(sub x)/L(sub Bol) decreases sharply with spectral types later than B1, reaching values of about 10(exp -9) at B3 V; much less than the value of 10(exp -7) that holds for O stars and early-B stars. The survey includes four beta Cephei stars and two Be stars. Our observations are consistent with the finding that beta Cephei variables have softer spectra than other stars of the same spectral type. The X-ray emission measures for the stars are compared with upper and lower limits derived using mass loss rates and terminal velocities from line-driven wind theory. It is concluded that if shocks embedded in the winds are the source of the X-ray emission then a significant fraction of the winds in B stars must be hot. One to a few shocks can account for the observed emission measures. As a function of spectral type, there appears to be a transition in X-ray emission properties at about B1 to B1.5, with later type stars having a smaller L(sub x)/L(sub Bol) ratio. Coronal and shock models are discussed in regards to the BO V star tau Sco which has an anomalously high source temperature.