We derive the radii of 16 brown dwarfs observed by AKARI using their parallaxes and the ratios of observed to model fluxes. We find that the brown dwarf radius ranges between 0.64-1.13 R sub(J) with ...an average radius of 0.83 R sub(J). We find a trend in the relation between radii and T sub(eff); the radius is at a minimum at T sub(eff) ~ 1600 K, which corresponds to the spectral types of mid- to late-L. The result is interpreted by a combination of radius-mass and radius-age relations that are theoretically expected for brown dwarfs older than 10 super(8) yr.
The detection of the CO sub(2) absorption band at 4.2 mu m in brown dwarf spectra by AKARI has made it possible to discuss CO sub(2) molecular abundance in brown dwarf atmospheres. In our previous ...studies, we found an excess in the 4.2 mu m CO sub(2) absorption band of three brown dwarf spectra, and suggested that these deviations were caused by high C and O elemental abundances in their atmospheres. To validate this hypothesis, we have constructed a set of models of brown dwarf atmospheres with various elemental abundance patterns, and we investigate the variations of the molecular composition and the thermal structure, and how they affect the near-infrared spectra between 1.0 and 5.0 mu m. The 4.2 mu m CO sub(2) absorption band in some late-L and T dwarfs taken by AKARI is stronger or weaker than predicted by corresponding models with solar abundance. By comparing the CO sub(2) band in the model spectra to the observed near-infrared spectra, we confirm possible elemental abundance variations among brown dwarfs. We find that the band strength is especially sensitive to O abundance, but C is also needed to reproduce the entire near-infrared spectra. This result indicates that both the C and O abundances should increase and decrease simultaneously for brown dwarfs. We find that a weaker CO sub(2) absorption band in a spectrum can also be explained by a model with lower "C and O" abundances.
We propose that the 2.7-μm H2O, 3.3-μm CH4 and 4.6-μm CO absorption bands can be good tracers of chromospheric activity in brown dwarfs. In our previous study, we found that there are difficulties in ...explaining entire spectra between 1.0 and 5.0 μm with the unified cloudy model (UCM), a brown dwarf atmosphere model. Based on simple radiative equilibrium, temperature in a model atmosphere usually decreases monotonically with height. However, if a brown dwarf has a chromosphere, as inferred by some observations, the temperature in the upper atmosphere is higher. We construct a simple model that takes into account heating owing to chromospheric activity by setting a temperature floor in the upper atmosphere, and find that the model spectra of three brown dwarfs with moderate Hα emission, an indicator of chromospheric activity, are considerably improved to match the AKARI spectra. Because of the higher temperatures in the upper atmosphere, the number of CH4 molecules is reduced, and the absorption band strengths become weaker. The strengths of the absorption bands of H2O and CO also become weaker. On the other hand, other objects with weak Hα emission cannot be fitted with our treatment. We also briefly discuss magnetic heating processes that possibly operate in the upper atmosphere, by extending our numerical simulations for the Sun and stars with surface convection to brown dwarf atmospheres.
We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (>10 keV) properties for local active galactic nuclei (AGNs). The Swift Burst Alert ...Telescope all-sky survey provides an unbiased, flux-limited selection of hard X-ray-detected AGNs. Cross-correlating the 22 month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGNs detected by the AKARI instruments. We find a strong correlation for most AGNs between the infrared (9, 18, and 90 mu m) and hard X-ray (14-195 keV) luminosities, and quantify the correlation for various subsamples of AGNs. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1 galaxies, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick (CT) sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity versus infrared color diagram, in which type 1 radio-loud AGNs are well isolated from the others in the sample. The other uses the X-ray versus infrared color as a useful redshift-independent indicator for identifying CT AGNs. Importantly, CT AGNs and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR.
We present ESO/VLT spectra in the 2.9-4.1 μm range for a large sample of infrared stars in the Large Magellanic Cloud (LMC), selected on the basis of MSX and 2MASS colours to be extremely ...dust-enshrouded AGB star candidates. Out of 30 targets, 28 are positively identified as carbon stars, significantly adding to the known population of optically invisible carbon stars in the LMC. We also present spectra for six IR-bright stars in or near three clusters in the LMC, identifying four of them as carbon stars and two as oxygen-rich supergiants. We analyse the molecular bands of C2H2 at 3.1 and 3.8 μm, HCN at 3.57 μm, and sharp absorption features in the 3.70-3.78 μm region that we attribute to C2H2. There is evidence for a generally high abundance of C2H2 in LMC carbon stars, suggestive of high carbon-to-oxygen abundance ratios at the low metallicity in the LMC. The low initial metallicity is also likely to have resulted in less abundant HCN and CS. The sample of IR carbon stars exhibits a range in C2H2:HCN abundance ratio. We do not find strong correlations between the properties of the molecular atmosphere and circumstellar dust envelope, but the observed differences in the strengths and shapes of the absorption bands can be explained by differences in excitation temperature. High mass-loss rates and strong pulsation would then be seen to be associated with a large scale height of the molecular atmosphere.
Studies have shown that long-term (5alpha,6alpha)-7,8-didehydro-4,5-epoxy-17-methylmorphinan-3,6-diol (morphine) treatment increases the sensitivity to painful heat stimuli (thermal hyperalgesia). ...The cellular adaptations contributing to sustained morphine-mediated pain sensitization are not fully understood. It was shown previously (J Neurosci 22:6747-6755, 2002) that sustained morphine exposure augments pain neurotransmitter such as calcitonin gene-related peptide (CGRP) release in the dorsal horn of the spinal cord in response to the heat-sensing transient receptor potential vanilloid 1 receptor agonist 8-methyl-N-vanillyl-6-nonenamide (capsaicin). In the present study, we demonstrate that sustained morphine-mediated augmentation of CGRP release from isolated primary sensory dorsal root ganglion neurons is dependent on protein kinase A and Raf-1 kinase. Our data indicate that, in addition to neural system adaptations, sustained opioid agonist treatment also produces intracellular compensatory adaptations in primary sensory neurons, leading to augmentation of evoked pain neurotransmitter release from these cells.
The dependence of stellar molecular bands on the metallicity is studied using infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and M-type supergiants in the Large and Small ...Magellanic Clouds (LMC and SMC) and in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB stars. The equivalent width of acetylene is found to be high even at low metallicity. The high C2H2 abundance can be explained with a high carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast, the HCN equivalent width is low: fewer than half of the extra-galactic carbon stars show the 3.5 μm HCN band, and only a few LMC stars show high HCN equivalent width. HCN abundances are limited by both nitrogen and carbon elemental abundances. The amount of synthesized nitrogen depends on the initial mass, and stars with high luminosity (i.e. high initial mass) could have a high HCN abundance. CH bands are found in both the extra-galactic and Galactic carbon stars. One SMC post-AGB star, SMC-S2, shows the 3.3 μm PAH band. This first detection of a PAH band from an SMC post-AGB star confirms PAHs can form in these low-metallicity stars. None of the oxygen-rich LMC stars show SiO bands, except one possible detection in a low quality spectrum. The limits on the equivalent widths of the SiO bands are below the expectation of up to 30 Å for LMC metallicity. Several possible explanations are discussed, mostly based on the effect of pulsation and circumstellar dust. The observations imply that LMC and SMC carbon stars could reach mass-loss rates as high as their Galactic counterparts, because there are more carbon atoms available and more carbonaceous dust can be formed. On the other hand, the lack of SiO suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich stars. The effect on the ISM dust enrichment is discussed.
Using a recently developed method (Salamon, Z., Macleod, H. A., and Tollin, G. (1997) Biophys. J. 73, 2791–2797), plasmon-waveguide resonance spectroscopy, we have been able, for the first time, to ...directly measure the binding between the human brain δ-opioid receptor (hDOR) and its G-protein effectors in real-time. We have found that the affinity of the G-proteins toward the receptor is highly dependent on the nature of the ligand pre-bound to the receptor. The highest affinity was observed when the receptor was bound to an agonist (∼10 nm); the lowest when receptor was bound to an antagonist (∼500 nm); and no binding at all was observed when the receptor was bound to an inverse agonist. We also have found direct evidence for the existence of an additional G-protein binding conformational state that corresponds to the unliganded receptor, which has a G-protein binding affinity of ∼60 nm. Furthermore, GTP binding to the receptor·G-protein complex was only observed when the agonist was pre-bound. Similar studies were carried out using the individual G-protein subtypes for both the agonist and the unliganded receptor. Significant selectivity toward the different G-protein subtypes was observed. Thus, the unliganded receptor had highest affinity toward the Gαo (Kd ∼ 20 nm) and lowest affinity toward the Gαi2 (∼590 nm) subtypes, whereas the agonist-bound state had highest affinity for the Gαo and Gαi2 subtypes (Kd ∼ 9 nm and ∼ 7 nm, respectively). GTP binding was also highly selective, both with respect to ligand and G-protein subtype. We believe that this methodology provides a powerful new way of investigating transmembrane signaling.
ABSTRACT
Near‐ and mid‐IR survey data from DENIS and ISOGAL are used to investigate the structure and formation history of the inner 10° (1.4 kpc) of the Milky Way galaxy. Synthetic bolometric ...corrections and extinction coefficients in the near‐ and mid‐infrared (mid‐IR) are derived for stars of different spectral types, to allow the transformation of theoretical isochrones into observable colour–magnitude diagrams. The observed IR colour–magnitude diagrams are used to derive the extinction, metallicity and age for individual stars. The inner galaxy is dominated by an old population (≳7 Gyr). In addition, an intermediate‐age population (∼200 Myr–7 Gyr) is detected, which is consistent with the presence of a few hundred asymptotic giant branch stars with heavy mass loss. Furthermore, young stars (≲200 Myr) are found across the inner bulge. The metallicities of these stellar population components are discussed. These results can be interpreted in terms of an early epoch of intense star formation and chemical enrichment that shaped the bulk of the bulge and nucleus, and a more continuous star formation history that gradually shaped the disc from the accretion of subsolar metallicity gas from the halo. A possible increase in star formation ∼200 Myr ago might have been triggered by a minor merger. Ever since the formation of the first stars, mechanisms have been at play that mix the populations from the nucleus, bulge and disc. Luminosity functions across the inner Galactic plane indicate the presence of an inclined (bar) structure at ≳1 kpc from the Galactic Centre, near the inner Lindblad resonance. The innermost part of the bulge, within ∼1 kpc from the Galactic Centre, seems azimuthally symmetric.
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