Masses and Radii of the Nuclei with N>=Z in an Alpha-Cluster Model

In the framework of a recently developed alpha-cluster model a nucleus is represented as a core (alpha-cluster liquid drop with dissolved excess neutron pairs in it) and a nuclear molecule on its surface. From analysis of experimental nuclear binding energies one can find the number of alpha-clusters in the molecule and calculate the nuclear charge radii. It was shown that for isotopes of one Z with growing A the number of alpha-clusters in the molecule decreases to three, which corresponds to the nucleus 12C for even Z and 15N for odd Z, and the specific density of the core binding energy \rho grows and reaches its saturation value. In this paper it is shown that the value \rho=2.55 MeV/fm^3 explains the particular number of excess neutrons in stable nuclei.Comment: 7 pages, 3 eps figures, submitted as a contribution to the Proceedings of the International Conference, Messina, Italy, October 5-9, 200

A Systematic Study of X-Ray Flares from Low-Mass Young Stellar Objects in the Rho Ophiuchi Star-Forming Region with Chandra

We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using Chandra observations of the main region of the Rho Oph. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay. We derived the time-averaged temperature (kT), luminosity (L_X), rise and decay timescales (tau_r and tau_d) of the flares, finding that (1) class I-II sources tend to have a high kT, (2) the distribution of L_X during flares is nearly the same for all classes, and (3) positive and negative log-linear correlations are found between tau_r and tau_d, and kT and tau_r. In order to explain these relations, we used the framework of magnetic reconnection model to formulate the observational parameters as a function of the half-length of the reconnected magnetic loop (L) and magnetic field strength (B). The estimated L is comparable to the typical stellar radius of these objects (10^{10-11} cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (10^{12} cm) connecting the star with its inner accretion disk. The higher kT observed for class I sources may be explained by a higher magnetic field strength (about 500 G) than for class II-III sources (200-300 G).Comment: 33 pages, 7 figures, accepted for publication in PASJ, the complete version of tables are available at ftp://ftp-cr.scphys.kyoto-u.ac.jp/pub/crmember/kensuke/PASJ_RhoOph/KI_all.tar .g

Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies

We present the results on millimeter interferometric observations of four luminous infrared galaxies (LIRGs), Arp 220, Mrk 231, IRAS 08572+3915, and VV 114, and one Wolf-Rayet galaxy, He 2-10, using the Nobeyama Millimeter Array (NMA). Both the HCN(1-0) and HCO+(1-0) molecular lines were observed simultaneously and their brightness-temperature ratios were derived. High-quality infrared L-band (2.8-4.1 micron) spectra were also obtained for the four LIRGs to better constrain their energy sources deeply buried in dust and molecular gas. When combined with other LIRGs we have previously observed with NMA, the final sample comprised nine LIRGs (12 LIRGs' nuclei) with available interferometric HCN(1-0) and HCO+(1-0) data-sufficient to investigate the overall trend in comparison with known AGNs and starburst galaxies. We found that LIRGs with luminous buried AGN signatures at other wavelengths tend to show high HCN(1-0)/HCO+(1-0) brightness-temperature ratios as seen in AGN-dominated galaxies, while the Wolf-Rayet galaxy He 2-10 displays a small ratio. An enhanced HCN abundance in the interstellar gas surrounding a strongly X-ray-emitting AGN, as predicted by some chemical calculations, is a natural explanation of our results.Comment: 43 pages, 11 figures, accepted for publication in Astronomical Journal. Higher resolution version is available at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN2/HCN2.pd

HCN to HCO^+ Millimeter Line Diagnostics of AGN Molecular Torus I : Radiative Transfer Modeling

We explore millimeter line diagnostics of an obscuring molecular torus modeled by a hydrodynamic simulation with three-dimensional nonLTE radiative transfer calculations. Based on the results of high-resolution hydrodynamic simulation of the molecular torus around an AGN, we calculate intensities of HCN and HCO^{+} rotational lines as two representative high density tracers. The three-dimensional radiative transfer calculations shed light on a complicated excitation state in the inhomogeneous torus, even though a spatially uniform chemical structure is assumed. Our results suggest that HCN must be much more abundant than HCO^{+} in order to obtain a high ratio ($R_{HCN/HCO+}\sim 2$) observed in some of the nearby galaxies. There is a remarkable dispersion in the relation between integrated intensity and column density, indicative of possible shortcomings of HCN(1-0) and HCO^{+}(1-0) lines as high density tracers. The internal structures of the inhomogeneous molecular torus down to subparsec scale in external galaxies will be revealed by the forthcoming Atacama Large Millimeter/submillimeter Array (ALMA). The three-dimensional radiative transfer calculations of molecular lines with high-resolution hydrodynamic simulation prove to be a powerful tool to provide a physical basis for molecular line diagnostics of the central regions of external galaxies.Comment: 29 pages, 13 figures, Accepted for publication in ApJ, For high resolution figures see http://alma.mtk.nao.ac.jp/~masako/MS72533v2.pd

Near-infrared K-band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples

We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert 2 galaxies in the CfA and 12 micron samples. The strength of the CO absorption features at 2.3-2.4 micron produced by stars is measured in terms of a spectroscopic CO index. A clear anti-correlation between the observed CO index and the nuclear K-L color is present, suggesting that a featureless hot dust continuum heated by an AGN contributes significantly to the observed K-band fluxes in the nuclei of Seyfert 2 galaxies. After correction for this AGN contribution, we estimate nuclear stellar K-band luminosities for all sources, and CO indices for sources with modestly large observed CO indices. The corrected CO indices for 10 (=40%) Seyfert 2 nuclei are found to be as high as those observed in star-forming or elliptical (=spheroidal) galaxies. We combine the K-band data with measurements of the L-band 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission feature, another powerful indicator for star-formation, and find that the 3.3 micron PAH to K-band stellar luminosity ratios are substantially smaller than those of starburst galaxies. Our results suggest that the 3.3 micron PAH emission originates in the putative nuclear starbursts in the dusty tori surrounding the AGNs, because of its high surface brightness, whereas the K-band CO absorption features detected at the nuclei are dominated by old bulge (=spheroid) stars, and thus may not be a powerful indicator for the nuclear starbursts. We see no clear difference in the strength of the CO absorption and PAH emission features between the CfA and 12 micron Seyfert 2s.Comment: 28 pages, 6 figures, accepted for publication in ApJ (10 October 2004, v614 issue

Survival in Cats with Naturally Occurring Chronic Kidney Disease (2000–2002)

Duration of survival of cats with naturally occurring chronic kidney disease (CKD) is poorly characterized. Hypothesis : Stage of kidney disease based on serum creatinine concentration (SCr) at the time of diagnosis and after correction of prerenal azotemia is strongly associated with duration of survival in cats. Animals : Two hundred and eleven client-owned cats with naturally occurring CKD evaluated between April 2000 and January 2002. Methods : Retrospective case review of 733 cats with SCr > 2.3 mg/dL. Examination of the medical records identified 211 cats that met all other inclusion and exclusion criteria for this study. Clinical characteristics, clinicopathologic data, and survival times were extracted from the medical record. Owners and referring veterinarians were contacted by phone to obtain follow-up if it was not documented in the record. Kaplan-Meier survival curves were performed to determine survival times for International Renal Interest Society (IRIS) stage both at diagnosis and at baseline (ie, after correction of prerenal azotemia). Results : Median survival for cats in IRIS stage IIb at the time of diagnosis was 1,151 days (range 2–3,107), and was longer than survival in stage III (median 778, range 22–2,100) or stage IV (median 103, range 1–1,920) ( P -value < .0001). P -value for effect of stage at diagnosis was <.0001. Conclusions and Clinical Importance : IRIS stage of CKD based on serum creatinine at the time of diagnosis is strongly predictive of survival in cats with naturally occurring CKD.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75440/1/j.1939-1676.2008.0163.x.pd

Millimeter Interferometric Investigations of the Energy Sources of Three Ultraluminous Infrared Galaxies, UGC 5101, Mrk 273, and IRAS 17208-0014, based on HCN to HCO+ Ratios

We present interferometric observations of three ultraluminous infrared galaxies (ULIRGs; UGC 5101, Mrk 273, and IRAS 17208-0014) in the 3-mm wavelength range, using the Nobeyama Millimeter Array. Both the HCN (J=1-0) and HCO+ (J=1-0) molecular lines were observed simultaneously. HCN emission was clearly detected at the nuclear positions of these ULIRGs, and HCO+ emission was detected at the nuclear positions of UGC 5101 and IRAS 17208-0014. The HCN to HCO+ brightness-temperature ratios toward the nuclei of the three ULIRGs were derived and compared with those of lower luminosity galaxies known to be dominated by active galactic nuclei (AGNs) or starbursts. In UGC 5101 and Mrk 273, where there is evidence for obscured AGNs from previous observations at other wavelengths, we found high HCN/HCO+ ratios (>1.8) that are in the range found for AGN-dominated galaxies. In IRAS 17208-0014, where the presence of a powerful obscured AGN has been unclear, the ratio (1.7) is in between the observed values for starburst- and AGN-dominated galaxies. The high HCN/HCO+ brightness-temperature ratios in UGC 5101 and Mrk 273 could be the consequence of an HCN abundance enhancement, which is expected from chemical effects of the central X-ray emitting AGN on the surrounding dense molecular gas. Our proposed millimeter interferometric method based on HCN/HCO+ ratios may be an effective tool for unveiling elusive buried AGNs at the cores of ULIRGs, especially because of the negligible dust extinction at these wavelengths.Comment: 15 pages (emulateapj.sty), 8 figures (figures 1-5 resolution reduced), Accepted for publication in Astronomical Journal, A PDF file with high resolution is availble at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN/HCN.pd