The night-sky at the Calar Alto Observatory II: The sky at the near infrared

We present here the characterization of the night sky-brightness at the near-infrared, the telescope seeing, and the fraction of useful time at the Calar Alto observatory. For this study we have collected a large dataset comprising 7311 near-infrared images taken regularly along the last four years for the ALHAMBRA survey (J, H and Ks-bands), together with a more reduced dataset of additional near-infrared images taken for the current study. In addition we collected the information derived by the meteorological station at the observatory during the last 10 years, together with the results from the cloud sensor for the last ~2 years. We analyze the dependency of the near-infrared night sky-brightness with the airmass and the seasons, studying its origins and proposing a zenithal correction. A strong correlation is found between the night sky-brightness in the Ks-band and the air temperature, with a gradient of ~ -0.08 mag per 1 C degree. The typical (darkest) night sky-brightness in the J, H and Ks-band are 15.95 mag (16.95 mag), 13.99 mag (14.98 mag) and 12.39 mag (13.55 mag), respectively. These values show that Calar Alto is as dark in the near-infrared as most of the other astronomical astronomical sites in the world that we could compare with. Only Mauna Kea is clearly darker in the Ks-band. The typical telescope seeing at the 3.5m is ~1.0" when converted to the V-band, being only slightly larger than the atmospheric seeing measured at the same time by the seeing monitor, ~0.9". Finally we estimate the fraction of useful time based on the relative humidity, gust wind speed and presence of clouds. This fraction, ~72%, is very similar to the one derived in Paper I, based on the fraction of time when the extinction monitor is working.Comment: 15 pages, 6 figures, accepted to be published in PAS

Analysis of the Interaction Effects in the Southern Galaxy Pair Tol1238-364 and ESO381-G009

In the context of the connection among galaxy-galaxy interaction, starbursts and nuclear activity, we present and discuss a quantitative morphological analysis based on BVR images and a detailed spectroscopic investigation of two interacting galaxies, the Seyfert 2 Tol1238-364 (IC 3639) and its companion ESO381-G009, forming a triple system with ESO381-G006. Broad-band optical photometry is complemented by Halpha imaging, which provides information about the distribution of star forming regions across the galaxies. Long-slit spectroscopic data obtained at different position angles of the slit are employed to determine the physical conditions of circumnuclear and extranuclear regions. A mixture of thermal and non-thermal ionizing radiation is found in the surroundings of the nucleus of Tol1238-364 and the energy budget supports the presence of a circumnuclear starburst.Several regions in both the galaxies show anomalous line ratios: additional ionization by shock-heating and low ionization of some extranuclear HII regions are suggested as possible explanations. An analysis of the emission-line profiles reveals the presence of a broad Halpha component in the nuclear region of Tol1238-364. Independent estimates of the star formation rates (SFR) were obtained through flux-calibrated Halpha-images and FIR emission in the four IRAS bands. Overall SFR densities have been compared with the SFR densities derived from Halpha emission in the individual regions of the galaxies sampled by long-slit spectra. In both galaxies an enhancement of the star formation activity with respect to isolated galaxies is revealed. The prevalence of starburst or nuclear activity has been examined through FIR color indices. The interaction scenario is discussed on the basis of the observed galaxy properties.Comment: Tentatively scheduled for publication in ApJS, v184 n2 October 2003 issue. A version with full resolution figures is available as unedited preprint at http://www.journals.uchicago.edu/ApJ/future.htm

Evolutionary analysis implicates RNA polymerase II pausing and chromatin structure in nematode piRNA biogenesis

Piwi-interacting RNAs (piRNAs) control transposable elements widely across metazoans but have rapidly evolving biogenesis pathways. In Caenorhabditis elegans, almost all piRNA loci are found within two 3Mb clusters on Chromosome IV. Each piRNA locus possesses an upstream motif that recruits RNA polymerase II to produce a ~28 nt precursor transcript. Here, we use comparative epigenomics across nematodes to gain insight into piRNA biogenesis. We show that the piRNA upstream motif is derived from core promoter elements controlling snRNA biogenesis. We describe two alternative modes of piRNA organisation in nematodes: in C. elegans and closely related nematodes, piRNAs are clustered within repressive H3K27me3 chromatin, whilst in other species, typified by Pristionchus pacificus, piRNAs are distributed genome-wide within introns of actively transcribed genes. In both groups, piRNA production depends on downstream sequence signals associated with RNA polymerase II pausing, which synergise with the chromatin environment to control piRNA precursor transcription

First optical identification of a suprsoft X-ray source in M31

We propose the first association of an optical counterpart with a luminous supersoft X-ray source in M31, RX J0044.0+4118, observed with ROSAT in July 1991. The PSPC position is at 1.6" angular distance from a candidate nova in outburst in September of 1990. This is interesting because the incidence of classical novae among supersoft X-ray sources is an open question. The proposed optical counterpart was measured at R~17.7 in September of 1990, and it had faded to R>19.2 when it was observed again after 70 days. The light curve was too sparsely monitored for definite conclusions on the speed class of the nova. No other variable objects with V<23.5 were found in the ROSAT spatial error box. We evaluate that the probability that a classical or recurrent nova was in outburst in the ROSAT error box in the few years preceding the observation is very small, so the proposed identification is meaningful. We also show evidence that the associated supersoft X-ray source turned off in the third year after the outburst.Comment: To appear in Astronomy and Astrophysic

The abundance of natural arsenic in deep thermal fluids of geothermal and petroleum reservoirs in Mexico

The lack of chemical similarity between thermal fluids in geothermal and petroleum reservoirs in Mexico indicates a distinct origin for arsenic (As) in both systems. Deep fluids from geothermal reservoirs along the Transmexican volcanic belt are characterized by elevated As concentrations, within an average range of 1 to 100 mg/l at a depth from 600 to 3000mb.s.l. The lack of correlation between As and salinity reflects the importance of secondary water-rock interaction processes. The predominance of As compared to Fe and Cu concentrations, and the abundance of secondary minerals in temperature-dependent hydrothermal zones, support this hypothesis. Oilfield waters from sedimentary basins in SE-Mexico show maximum As concentrations of 2 mg/l, at a depth from 2900 to 6100 m b.s.l. The linear Cl−/As correlation for oilfield waters indicates that As input occurs during the mixing between meteoric water and evaporated sea-water, and that there is only minor As derived from interaction with carbonate host rock

The Merging Seyfert Galaxies MARKARIAN:423 and MARKARIAN:739

In this paper long slit spectroscopy and broad band imaging of the intermediate Seyfert galaxies Mkn 423 and Mkn 739 are presented. The analysis of the extranuclear emissions reveals that Mkn 423 and Mkn 739 are undergoing a strong burst of star formation spread over a kpc-sized scale. Although the morphological appearance of Mkn 423 is suggestive of a galaxy of type Sa/SBa with a giant HII region (component B), the peculiar kinematics of Mkn 423 and the very large H\u3b1 luminosity of component B suggest that this system could be the result of an ongoing merging of two galaxies. The resolution ~2 A FWHM of the spectra taken in the range 4000-5500 A allowed to resolve substructures in the H\u3b2 and [OIII]\u3bb\u3bb4959,5007 line profiles, permitting an analysis of the circumnuclear regions of these objects. The narrow line spectrum of Mkn 423 originates in two partially resolved blobs, of high ionization degree, which are likely to be the optical counterpart of two radio emitting sources or which are associated with the NLR and circumnuclear gas ionized by the central source. Mkn 739 shows extended high-ionization gas up to a distance ~4 h^-1^ kpc from the Seyfert nucleus. This gas is photoionized by the active nucleus itself, and it is in a kinematical status (probably in outflow) different from that of the low ionization gas associated with star formation. The high ionization degree observed as far as ~2 h^-1^ kpc from the Seyfert nucleus suggests that the central ionizing source is most probably anisotropic