Infrared Telescope Facility Research Articles

TRANSITIONAL DISKS AND THEIR ORIGINS: AN INFRARED SPECTROSCOPIC SURVEY OF ORION A

Transitional disks are protoplanetary disks around young stars, with inner holes or gaps which are surrounded by optically thick outer, and often inner, disks. Here we present observations of 62 new transitional disks in the Orion A star-forming region. These were identified using the \textit{Spitzer Space Telescope}'s Infrared Spectrograph and followed up with determinations of stellar and accretion parameters using the Infrared Telescope Facility's SpeX. We combine these new observations with our previous results on transitional disks in Taurus, Chamaeleon I, Ophiuchus and Perseus, and with archival X-ray observations. This produces a sample of 105 transitional disks of "cluster" age 3 Myr or less, by far the largest hitherto assembled. We use this sample to search for trends between the radial structure in the disks and many other system properties, in order to place constraints on the possible origins of transitional disks. We see a clear progression of host star accretion rate and the different disk morphologies. We confirm that transitional disks with complete central clearings have median accretion rates an order of magnitude smaller than radially continuous disks of the same population. Pre-transitional disks --- those objects with gaps that separate inner and outer disks --- have median accretion rates intermediate between the two. Our results from the search for statistically significant trends, especially related to $\dot{M}$, strongly support that in both cases the gaps are far more likely to be due to the gravitational influence of Jovian planets or brown dwarfs orbiting within the gaps, than to any of the photoevaporative, turbulent or grain-growth processes that can lead to disk dissipation. We also find that the fraction of Class II YSOs which are transitional disks is large, 0.1-0.2, especially in the youngest associations.

Erratum: Molecular hydrogen and [Fe ii] in active galactic nuclei III: LINERS and star forming galaxies

We study the kinematics and excitation mechanisms of H2 and [Fe II] lines in a sample of 67 emission-line galaxies with Infrared Telescope Facility SpeX near-infrared (NIR, 0.8-2.4 micrometers) spectroscopy together with new photoionisation models. H2 emission lines are systematically narrower than narrow-line region (NLR) lines, suggesting that the two are, very likely, kinematically disconnected. The new models and emission-line ratios show that the thermal excitation plays an important role not only in active galactic nuclei but also in star forming galaxies. The importance of the thermal excitation in star forming galaxies may be associated with the presence of supernova remnants close to the region emitting H2 lines. This hypothesis is further supported by the similarity between the vibrational and rotational temperatures of H2. We confirm that the diagram involving the line ratios H2 2.121/Br_gamma and [Fe II] 1.257/Pa_beta is an efficient tool for separating emission-line objects according to their dominant type of activity. We suggest new limits to the line ratios in order to discriminate between the different types of nuclear activity.

Jupiter's aurora in ultraviolet and infrared: Simultaneous observations with the Hubble Space Telescope and the NASA Infrared Telescope Facility

We compare Jupiter's northern auroral emissions in infrared (IR) and ultraviolet (UV) using ground‐based IR observations from the NASA Infrared Telescope Facility and UV observations from Hubble Space Telescope on 16 December 2000, the only date for which simultaneous observations in the two wavelength regions exist. We use polar projections and longitudinal brightness cuts to compare the IR ( ions) and UV (H2, H, and Lyman‐alpha) aurorae, consisting of the main auroral emission, emission regions both poleward and equatorward of the main emission, and those associated with the Io footprint and its extended tail. We demonstrate that (1) the IR main emission and the equatorward diffuse emissions are generally good proxies for the UV and vice versa, (2) the spatial distribution and temporal behavior of UV and IR emissions within the main emission, at high magnetic latitudes, differ substantially, (3) UV and IR emissions associated with the Io interaction appear at the Io footprint and along an extended (downstream) tail but differ in relative brightness. While the UV aurora is excited directly, the IR aurora is a thermal emission, its intensity depends on both the number density of the ions and the temperature. Three main factors may contribute to the observed morphological differences of the simultaneous emissions in the two wavelengths, namely ion transport, local heating, and the energy of the precipitating electrons. We estimate the ion transport distances, based on the ion lifetime and suggest that ion transport cannot account for large‐scale morphological differences between the UV and IR emissions. We propose that neutral gas heating by particle precipitation and Joule heating locally enhances the emission with no UV counterpart. Additionally, we estimate that local temperature variations are reflected in the IR emission with a time lag of several hours with respect to the UV. Finally, high precipitating electron energies exceeding a certain value might lead to chemical loss of the low altitude ions, suppress the lower IR emitting layers, and contribute to the observed differences of the emissions between the two wavelength regimes.

Spatial distribution of water in the stratosphere of Jupiter fromHerschelHIFI and PACS observations

Context. In the past 15 years, several studies suggested that water in the stratosphere of Jupiter originated from the Shoemaker-Levy 9 (SL9) comet impacts in July 1994, but a direct proof was missing. Only a very sensitive instrument observing with high spectral/spatial resolution can help to solve this problem. This is the case of the Herschel Space Observatory, which is the first telescope capable of mapping water in Jupiter’s stratosphere.Aims. We observed the spatial distribution of the water emission in Jupiter’s stratosphere with the Heterodyne Instrument for the Far Infrared (HIFI) and the Photodetector Array Camera and Spectrometer (PACS) onboard Herschel to constrain its origin. In parallel, we monitored Jupiter’s stratospheric temperature with the NASA Infrared Telescope Facility (IRTF) to separate temperature from water variability.Methods. We obtained a 25-point map of the 1669.9 GHz water line with HIFI in July 2010 and several maps with PACS in October 2009 and December 2010. The 2010 PACS map is a 400-point raster of the water 66.4 μ m emission. Additionally, we mapped the methane ν 4 band emission to constrain the stratospheric temperature in Jupiter in the same periods with the IRTF.Results. Water is found to be restricted to pressures lower than 2 mbar. Its column density decreases by a factor of 2−3 between southern and northern latitudes, consistently between the HIFI and the PACS 66.4 μ m maps. We infer that an emission maximum seen around 15 °S is caused by a warm stratospheric belt detected in the IRTF data. Conclusions. Latitudinal temperature variability cannot explain the global north-south asymmetry in the water maps. From the latitudinal and vertical distributions of water in Jupiter’s stratosphere, we rule out interplanetary dust particles as its main source. Furthermore, we demonstrate that Jupiter’s stratospheric water was delivered by the SL9 comet and that more than 95% of the observed water comes from the comet according to our models.

THE EARLIEST NEAR-INFRARED TIME-SERIES SPECTROSCOPY OF A TYPE Ia SUPERNOVA

We present ten medium-resolution, high signal-to-noise ratio near-infrared (NIR) spectra of SN 2011fe from SpeX on the NASA Infrared Telescope Facility (IRTF) and Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, obtained as part of the Carnegie Supernova Project. This data set constitutes the earliest time-series NIR spectroscopy of a Type Ia supernova (SN Ia), with the first spectrum obtained at 2.58 days past the explosion and covering -14.6 to +17.3 days relative to B-band maximum. C I {\lambda}1.0693 {\mu}m is detected in SN 2011fe with increasing strength up to maximum light. The delay in the onset of the NIR C I line demonstrates its potential to be an effective tracer of unprocessed material. For the first time in a SN Ia, the early rapid decline of the Mg II {\lambda}1.0927 {\mu}m velocity was observed, and the subsequent velocity is remarkably constant. The Mg II velocity during this constant phase locates the inner edge of carbon burning and probes the conditions under which the transition from deflagration to detonation occurs. We show that the Mg II velocity does not correlate with the optical light-curve decline rate {\Delta}m15. The prominent break at ~1.5 {\mu}m is the main source of concern for NIR k-correction calculations. We demonstrate here that the feature has a uniform time evolution among SNe Ia, with the flux ratio across the break strongly correlated with {\Delta}m15. The predictability of the strength and the onset of this feature suggests that the associated k-correction uncertainties can be minimized with improved spectral templates.

Molecular hydrogen and [Fe ii] in active galactic nuclei – III. Low-ionization nuclear emission-line region and star-forming galaxies

We study the kinematics and excitation mechanisms of H2 and [Fe II] lines in a sample of 67 emission-line galaxies with Infrared Telescope Facility SpeX near-infrared (NIR, 0.8-2.4 micrometers) spectroscopy together with new photoionisation models. H2 emission lines are systematically narrower than narrow-line region (NLR) lines, suggesting that the two are, very likely, kinematically disconnected. The new models and emission-line ratios show that the thermal excitation plays an important role not only in active galactic nuclei but also in star forming galaxies. The importance of the thermal excitation in star forming galaxies may be associated with the presence of supernova remnants close to the region emitting H2 lines. This hypothesis is further supported by the similarity between the vibrational and rotational temperatures of H2. We confirm that the diagram involving the line ratios H2 2.121/Br_gamma and [Fe II] 1.257/Pa_beta is an efficient tool for separating emission-line objects according to their dominant type of activity. We suggest new limits to the line ratios in order to discriminate between the different types of nuclear activity.

Uranus’ cloud particle properties and latitudinal methane variation from IRTF SpeX observations

The Uranian atmosphere was observed in August 2009 from 0.8 to 1.8 μm using the near-infrared spectrometer, SpeX, at NASA’s Infrared Telescope Facility. The observations had a spectral resolution of R=1200 and an average seeing of between 0.5″ in the H-Band (1.4–1.8μm) and 0.6″ in the I-Band (0.8–0.9μm). The reduced data were analyzed with a multiple-scattering retrieval code. We were able to reproduce observations when using a vertically-compact cloud in the upper troposphere and a vertically-extended, optically-thin haze above the 1-bar level. The existence of these two clouds is consistent with previous studies.The sub-micron portion of the data are most sensitive to very small scattering particles, allowing more insight into particle size than other portions of the infrared spectrum. This portion of the spectrum was therefore of particular interest and was not available in most previous studies of the planet. We assumed the particles in both clouds to be relatively strong forward scatterers (with a Henyey-Greenstein asymmetry factor of g=0.7). Given this assumption, we found single-scattering albedos in the tropospheric cloud particles to be ω¯=0.7 at wavelengths above 1.4μm and to gradually increase to ω¯=1.0 at wavelengths shortward of 1.0μm. In the upper haze, we found single-scattering albedos to be ω¯=1.0 with the exception of a narrow drop at 1.0μm to ω¯=0.6. We found a preference for upper haze particle radii at r=0.10μm. Retrievals of base pressure, fractional scale height, and optical depth in both cloud layers showed the best agreement with data when the base pressure of the upper haze was fixed just above the tropospheric clouds, rather than at or above the tropopausal cold trap. We found that these same retrievals strongly preferred tropospheric cloud particles of 1.35-μm radii, and observed cloud top height to increase away from the equator in the case of latitudinally invariant methane abundance.Latitudinal methane variability was also considered, both through a reflectivity study at the 825-nm collision-induced hydrogen absorption feature, as well as through radiative transfer analysis, using forward modeling and retrievals of cloud properties and methane abundance. The data suggested that methane abundance above the tropospheric clouds increased when moving from the midlatitudes towards the equator by at least 9%. The peak of this equatorial methane enrichment was determined to be at 4±2° S latitude, having moved nearly 15° northward since a reflectance study of 2002 data (Karkoschka and Tomasko, 2009).

The NEO (175706) 1996 FG3 in the 2–4 μm spectral region: Evidence for an aqueously altered surface

We present observations of the binary near-Earth Asteroid (175706) 1996 FG3 in the 2–4μm spectral region, obtained on multiple nights using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We find evidence for an absorption band of ∼5–10% (depending on the night and details of continuum choice), diagnostic for hydrated/hydroxylated minerals on the asteroid surface. This demonstrates that the optical surface of 1996 FG3 has not been heated to dehydrating temperatures. Sample-return missions targeting 1996 FG3 will likely find relatively fresh areas for sampling.

The Infrared Telescope Facility (IRTF) spectral library:

Context. The near-infrared (NIR) wavelength range offers some unique spectral features, and it is less prone to the extinction than the optical one. Recently, the first flux calibrated NIR library of cool stars from the NASA Infrared Telescope Facility (IRTF) have become available, and it has not been fully exploited yet.

THE METALLICITY OF THE CM DRACONIS SYSTEM

The CM Draconis system comprises two eclipsing mid-M dwarfs of nearly equal mass in a 1.27-day orbit. This well-studied eclipsing binary has often been used for benchmark tests of stellar models, since its components are amongst the lowest mass stars with well-measured masses and radii (~ 1% relative precision). However, as with many other low-mass stars, non-magnetic models have been unable to match the observed radii and effective temperatures for CM Dra at the 5-10% level. To date, the uncertain metallicity of the system has complicated comparison of theoretical isochrones with observations. In this Letter, we use data from the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) to measure the metallicity of the system during primary and secondary eclipses, as well as out of eclipse, based on an empirical metallicity calibration in the H and K near-infrared (NIR) bands. We derive a [Fe/H] = -0.30 +- 0.12 that is consistent across all orbital phases. The determination of [Fe/H] for this system constrains a key dimension of parameter space when attempting to reconcile model isochrone predictions and observations.

IRTF observations of S complex and other asteroids: Implications for surface compositions, the presence of clinopyroxenes, and their relationship to meteorites

Abstract– We have obtained near‐infrared spectra for near‐Earth asteroids (NEA) and Main Belt asteroids by using NASA’s Infrared Telescope Facility. Most of the S complex classes of the Tholen‐Bus‐DeMeo scheme and the S(I)–S(VII) classes are represented. To help interpret the results, we examined visible/near‐IR spectra for ordinary chondrites. The unequilibrated ordinary chondrites (UOC) spectra contain a 2.3 μm feature which is absent in the spectra of the equilibrated ordinary chondrites (EOC). On the basis of literature data and new spectra low‐Ca clinopyroxenes, we suggest that the 2.3 μm in UOC is due to the presence of low‐Ca clinopyroxene in the UOC which is absent in EOC. While this difference can be seen in the raw spectra, we confirmed this observation using a modified Gaussian model (MGM) for spectral analysis. Both the UOC and the EOC plot in the S(IV) field of the band area ratio plot for asteroids. We suggest that many or most S(IV) asteroids have material resembling UOC on their surfaces. An internally heated ordinary chondrite parent object would have EOC material at depth and UOC material on the surface. Cosmic ray exposure ages, and K‐Ar ages for L chondrites, indicate that most EOC came from relatively few objects; however, the age distributions for UOC are unlike those of EOC. We suggest that while EOC come from the interiors of a limited number of S(IV) asteroids, the UOC come from the surfaces of a large number of S(IV) asteroids.

SPECTRAL CLASSIFICATION OF THE BRIGHTEST OBJECTS IN THE GALACTIC STAR-FORMING REGION W40

We present high S/N, moderate resolution near-infrared spectra, as well as 10 micron imaging, for the brightest members of the central stellar cluster in the W40 HII region, obtained using the SpeX and MIRSI instruments at NASA's Infrared Telescope Facility. Using these observations combined with archival Spitzer Space Telescope data, we have determined the spectral classifications, extinction, distances, and spectral energy distributions for the brightest members of the cluster. Of the eight objects observed, we identify four main sequence (MS) OB stars, two Herbig Ae/Be stars, and two low-mass young stellar objects. Strong HeI absorption at 1.083 micron in the MS star spectra strongly suggests that at least some of these sources are in fact close binaries. Two out of the four MS stars also show significant infrared excesses typical of circumstellar disks. Extinctions and distances were determined for each MS star by fitting model stellar atmospheres to the SEDs. We estimate a distance to the cluster of between 455 and 535 pc, which agrees well with earlier (but far less precise) distance estimates. We conclude that the late-O star we identify is the dominant source of LyC luminosity needed to power the W40 HII region and is the likely source of the stellar wind that has blown a large (~4 pc) pinched-waist bubble observed in wide field mid-IR images. We also suggest that 3.6 cm radio emission observed from some of the sources in the cluster is likely not due to emission from ultra-compact HII regions, as suggested in other work, due to size constraints based on our derived distance to the cluster. Finally, we also present a discussion of the curious source IRS 3A, which has a very strong mid-IR excess (despite its B3 MS classification) and appears to be embedded in a dusty envelope roughly 2700 AU in size.

Spectral and spin measurement of two small and fast-rotating near-Earth asteroids

In May 2012 two asteroids made near-miss “grazing” passes at distances of a few Earth-radii: 2012 KP24 passed at 9 Earth-radii and 2012 KT42 at only 3 Earth-radii. The latter passed inside the orbital distance of geosynchronous satellites. From spectral and imaging measurements using NASA’s 3-m Infrared Telescope Facility (IRTF), we deduce taxonomic, rotational, and physical properties. Their spectral characteristics are somewhat atypical among near-Earth asteroids: C-complex for 2012 KP24 and B-type for 2012 KT42, from which we interpret the albedos of both asteroids to be between 0.10 and 0.15 and maximum effective diameters of 20±6 and 6±1m, respectively. Among B-type asteroids, the spectrum of 2012 KT42 is most similar to 3200 Phaethon and 4015 Wilson–Harrington. Not only are these among the smallest asteroids spectrally measured, we also find they are among the fastest-spinning: 2012 KP24 completes a rotation in 2.5008±0.0006min and 2012 KT42 rotates in 3.634±0.001min.

HDO and SO2thermal mapping on Venus: evidence for strong SO2 variability

We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10–12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344–1370 cm −1 range (around 7.35 μm) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60–80 km). Four HDO lines and tens of SO2 lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO2 and SO2/CO2 line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H2O mixing ratio is found to be 1.5 +/−0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO2 maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO2 mixing ratio strongly varies on a timescale of 24 h. The maximum SO2 mixing ratio ranges between 75 +/−25 ppb and 125 +/−50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.

ICE MINERALOGY ACROSS AND INTO THE SURFACES OF PLUTO, TRITON, AND ERIS

We present three near-infrared spectra of Pluto taken with the Infrared Telescope Facility and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane–nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases—one highly diluted by nitrogen and the other rich in methane. For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1% ± 0.5%, 7.1% ± 0.4%, and 8.2% ± 0.3% for sub-Earth longitudes of 10°, 125°, and 257°. Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. For Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0% ± 0.1% and 5.3% ± 0.4% for sub-Earth longitudes of 138° and 314°. Application of the Wilcoxon rank sum test to our measurements finds the differences are not statistically significant. For Eris, we find a bulk, hemisphere-averaged, methane abundance of 10% ± 2%. Pluto, Triton, and Eris do not exhibit a trend in methane–nitrogen mixing ratio with depth into their surfaces over the few centimeter range probed by these observations. This result is contrary to the expectation that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth.

Constraining albedo, diameter and composition of near-Earth asteroids via near-infrared spectroscopy

We present a method to constrain the albedo and diameters of near-Earth asteroids (NEAs) based on thermal flux in their near-infrared spectra (0.7–2.5μm) using the Standard Thermal Model. Near-infrared spectra obtained with the SpeX instrument on NASA Infrared Telescope Facility are used to estimate the albedo and diameters of 12 NEAs (1992 JE, 1992 UY4, 1999 JD6, 2004 XP14, 2005 YY93, 2007 DS84, 2005 AD13, 2005 WJ56, 1999 JM8, 2005 RC34, 2003 YE45, and 2008 QS11). Albedo estimates were compared with average albedo for various taxonomic classes outlined by Thomas et al. (Thomas, C.A. et al. [2011]. Astron. J. 142(3)) and are consistent with their results. Spectral band parameters, like band centers, are derived and compared to spectra of laboratory mineral mixtures and meteorites to constrain their composition and possible meteorite analogs. Based on our study we estimate the albedos and diameters of these NEAs and compare them with those obtained by other techniques such as ground-based mid-infrared, Spitzer thermal infrared and Arecibo radar. Our results are broadly consistent with the results from other direct methods like radar. Determining the compositions of low albedo asteroids is a challenge due to the lack of deep silicate absorption features. However, based on weak absorption features and albedo, we suggest possible meteorite analogs for these NEAs, which include black chondrites, CM2 carbonaceous chondrites and enstatite achondrites. We did not find any specific trends in albedo and composition among the asteroids we observed.

Outer Main Belt asteroids: Identification and distribution of four 3-μm spectral groups

This paper examines the distribution and the abundance of hydrated minerals (any mineral that contains H2O or OH) on outer Main Belt asteroids spanning the 2.5<a<4.0AU region. The hypothesis we are testing is whether planetesimals that accreted closer to the Sun experienced a higher degree of aqueous alteration. We would expect then to see a gradual decline of the abundance of hydrated minerals among the outer Main Belt asteroids with increasing heliocentric distance (2.5<a<4.0AU). We measured spectra (0.8–2.5μm and 1.9–4.1μm) of 28 outer Main Belt asteroids using the SpeX spectrograph/imager at the NASA Infrared Telescope Facility (IRTF). We identified four groups on the basis of the shape and the band center of the 3-μm feature. The first group, which we call “sharp”, exhibits a sharp 3-μm feature, attributed to hydrated minerals (phyllosilicates). Most asteroids in this group are located in the 2.5<a<3.3AU region. The second group, which we call “Ceres-like”, consists of 10 Hygiea and 324 Bamberga. Like Asteroid Ceres, these asteroids exhibit a 3-μm feature with a band center of 3.05±0.01μm that is superimposed on a broader absorption feature from ∼2.8 to 3.7μm. The third group, which we call “Europa-like”, includes 52 Europa, 31 Euphrosyne, and 451 Patientia. Objects in this group exhibit a 3-μm feature with a band center of 3.15±0.01μm. Both the Ceres-like and Europa-like groups are concentrated in the 2.5<a<3.3AU region. The fourth group, which we call “rounded”, is concentrated in the 3.4<a<4.0AU region. Asteroids in this group are characterized by a rounded 3-μm feature, attributed to H2O ice. A similar rounded 3-μm feature was also identified in 24 Themis and 65 Cybele. Unlike the sharp group, the rounded group did not experience aqueous alteration. Of the asteroids observed in this study, 140 Siwa, a P-type, is the only one that does not exhibit a 3-μm feature. These results are important to constrain the nature and the degree of aqueous alteration in outer Main Belt asteroids.

The discovery of a debris disc around the DAV white dwarf PG 1541+651

Abstract To search for circumstellar discs around evolved stars, we targeted roughly 100 DA white dwarfs from the Palomar Green survey with the Peters Automated Infrared Imaging Telescope (PAIRITEL). Here we report the discovery of a debris disc around one of these targets, the pulsating white dwarf PG 1541+651 (KX Draconis, hereafter PG1541). We detect a significant flux excess around PG1541 in the K band. Follow-up near-infrared spectroscopic observations obtained at the NASA Infrared Telescope Facility and photometric observations with the warm Spitzer Space Telescope confirm the presence of a warm debris disc within 0.13–0.36 R⊙ (11–32 × the stellar radius) at an inclination angle of 60°. At Teff = 11 880 K, PG1541 is almost a twin of the DAV white dwarf G29-38, which also hosts a debris disc. All previously known dusty white dwarfs are of the DAZ/DBZ spectral type due to accretion of metals from the disc. High-resolution optical spectroscopy is needed to search for metal absorption lines in PG1541 and to constrain the accretion rate from the disc. PG1541 is only 55 pc away from the Sun and the discovery of its disc in our survey demonstrates that our knowledge of the nearby dusty white dwarf population is far from complete.

Mars mesospheric zonal wind around northern spring equinox from infrared heterodyne observations of CO 2

We present direct observations of Mars zonal wind velocities around northern spring equinox (L S = 336°, L S = 355°, L S = 42°) during martian year 27 and 29. Data was acquired by means of infrared heterodyne spectroscopy of CO 2 features at 959.3917 cm −1 (10.4232 μm) and 957.8005 cm −1 (10.4405 μm) using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) at the McMath–Pierce telescope of the National Solar Observatory on Kitt Peak in Arizona and the NASA Infrared Telescope Facility on Mauna Kea, Hawaii between 2005 and 2008. Winds were measured on the dayside of Mars with an unprecedented spatial resolution allowing sampling of up to nine independent latitudes over the martian disk. Retrieved wind velocities depend strongly on latitude and season with values ranging from 180 m/s prograde to −94 m/s retrograde. A comparison of the observational results to predicted values from the Mars Climate Database yield a reasonable agreement between modeling and observation.

Io’s atmosphere: Constraints on sublimation support from density variations on seasonal timescales using NASA IRTF/TEXES observations from 2001 to 2010

We present an analysis of 19 μm spectra of Io’s SO 2 atmosphere from the TEXES mid-infrared high spectral resolution spectrograph on NASA’s Infrared Telescope Facility, incorporating new data taken between January 2005 and June 2010 and a re-analysis of earlier data taken from November 2001 to January 2004. This is the longest set of contiguous observations of Io’s atmosphere using the same instrument and technique thus far. We have fitted all 16 detected blended absorption lines of the ν 2 SO 2 vibrational band to retrieve the subsolar values of SO 2 column abundance and the gas kinetic temperature. By incorporating an existing model of Io’s surface temperatures and atmosphere, we retrieve sub-solar column densities from the disk-integrated data. Spectra from all years are best fit by atmospheric temperatures <150 K. Best-fit gas kinetic temperatures on the anti-Jupiter hemisphere, where SO 2 gas abundance is highest, are low and stable, with a mean of 108 (±18) K. The sub-solar SO 2 column density between longitudes of 90–220° varies from a low of 0.61 (±0.145) × 10 −17 cm −2, near aphelion in 2004, to a high of 1.51 (±0.215) × 10 17 cm −2 in 2010 when Jupiter was approaching its early 2011 perihelion. No correlation in the gas temperature was seen with the increasing SO 2 column densities outside the errors. Assuming that any volcanic component of the atmosphere is constant with time, the correlation of increasing SO 2 abundance with decreasing heliocentric distance provides good evidence that the atmosphere is at least partially supported by frost sublimation. The SO 2 frost thermal inertias and albedos that fit the variation in atmospheric density best are between 150–1250 W m −2 s −1/2 K −1 and 0.613–0.425 respectively. Photometric evidence favors albedos near the upper end of this range, corresponding to thermal inertias near the lower end. This relatively low frost thermal inertia produces larger amplitude seasonal variations than are observed, which in turn implies a substantial additional volcanic atmospheric component to moderate the amplitude of the seasonal variations of the total atmosphere on the anti-Jupiter hemisphere. The seasonal thermal inertia we measure is unique both because it refers exclusively to the SO 2 frost surface component, and also because it refers to relatively deep subsurface layers (few meters) due to the timescales of many years, while previous studies have determined thermal inertias at shallower levels (few centimeters), relevant for timescales of ∼2 h (eclipse) or ∼2 days (diurnal curves).