STIS Spectral Imagery of the OB Stars in NGC 604: Describing the Extraction Technique for a Crowded Stellar Field

We have developed a data reduction procedure to extract multiple spectra from a single two-dimensional Space Telescope Imaging Spectrograph (STIS) image of a crowded stellar field. This paper provides a description of our new technique, utilizing a STIS ultraviolet spectral image, acquired with the G140L grating and the 52 arcsec x 2 arcsec aperture, sampling a concentration of O and B stars in the central region of the NGC 604 starburst in M33. The software routines can disentangle and produce reliable ultraviolet spectra of stars with angular separations as small as 0.055 arcsec. Use of the extraction slit, based upon our model of the spectral cross dispersion profile, generates spectra with slightly higher resolution than the STScI standard processing. Our results clearly show that the spectral imaging capability of STIS represents a powerful tool for studying luminous stars in the star-forming regions of the Local Group.Comment: LaTeX, 23 pages total (including 11 figures and 1 table). To be published in June 2003 of The Astronomical Journal. Companion paper to "STIS Spectral Imagery of the OB Stars in NGC 604: The Most Luminous Stars" by Bruhweiler, Miskey, & Smith Neubi

12^{12}C/13^{13}C ratio in planetary nebulae from the IUE archives

We investigated the abundance ratio of $^{12}$C/$^{13}$C in planetary nebulae by examining emission lines arising from \ion{C}{3} 2s2p ^3P_{2,1,0} \to 2s^2 ^1S_0. Spectra were retrieved from the International Ultraviolet Explorer archives, and multiple spectra of the same object were coadded to achieve improved signal-to-noise. The $^{13}$C hyperfine structure line at 1909.6 \AA was detected in NGC 2440. The $^{12}$C/$^{13}$C ratio was found to be $\sim4.4\pm$1.2. In all other objects, we provide an upper limit for the flux of the 1910 \AA line. For 23 of these sources, a lower limit for the $^{12}$C/$^{13}$C ratio was established. The impact on our current understanding of stellar evolution is discussed. The resulting high signal-to-noise \ion{C}{3} spectrum helps constrain the atomic physics of the line formation process. Some objects have the measured 1907/1909 flux ratio outside the low-electron density theoretical limit for $^{12}$C. A mixture of $^{13}$C with $^{12}$C helps to close the gap somewhat. Nevertheless, some observed 1907/1909 flux ratios still appear too high to conform to the presently predicted limits. It is shown that this limit, as well as the 1910/1909 flux ratio, are predominantly influenced by using the standard partitioning among the collision strengths for the multiplet $^1S_0$--$^3P_J$ according to the statistical weights. A detailed calculation for the fine structure collision strengths between these individual levels would be valuable.Comment: ApJ accepted: 19 pages, 3 Figures, 2 Table

HST Observations and Photoionization Modeling of the LINER Galaxy NGC 1052

We present a study of available Hubble Space Telescope (HST) spectroscopic and imaging observations of the low ionization nuclear emission line region (LINER) galaxy NGC 1052. The WFPC2 imagery clearly differentiates extended nebular Halpha emission from that of the compact core. Faint Object Spectrograph (FOS) observations provide a full set of optical and UV data (1200-6800 Angstroms). These spectral data sample the innermost region (0."86 x 0."86 ~ 82pc x 82pc) and exclude the extended Halpha emission seen in the WFPC2 image. The derived emission line fluxes allow a detailed analysis of the physical conditions within the nucleus. The measured flux ratio for Halpha/Hbeta, F{Halpha}/F{Hbeta}=4.53, indicates substantial intrinsic reddening, E(B-V)=0.42, for the nuclear nebular emission. This is the first finding of a large extinction of the nuclear emission line fluxes in NGC 1052. If the central ionizing continuum is assumed to be attenuated by a comparable amount, then the emission line fluxes can be reproduced well by a simple photoionization model using a central power law continuum source with a spectral index of alpha = -1.2 as deduced from the observed flux distribution. A multi-density, dusty gas gives the best fit to the observed emission line spectrum. Our calculations show that the small contribution from a highly ionized gas observed in NGC 1052 can also be reproduced solely by photoionization modeling. The high gas covering factor determined from our model is consistent with the assumption that our line of sight to the central engine is obscured.Comment: 23 pages, 7 Postscript figures, 1 jpeg figure ; uses aaspp4.sty, 11pt to appear in The Astrophysical Journa

Far-Ultraviolet Surveys of Globular Clusters: Hunting for the Products of Stellar Collisions and Near Misses

Globular clusters are gravitationally bound stellar systems containing on the order of 100,000 stars. Due to the high stellar densities in the cores of these clusters, close encounters and even physical collisions between stars are inevitable. These dynamical interactions can produce exotic types of single and binary stars that are extremely rare in the galactic field, but which may be important to the dynamical evolution of their host clusters. A common feature of these dynamically-formed stellar populations is that many of their members are relatively hot, and thus bright in the far-ultraviolet (FUV) waveband. In this short review, I describe how space-based FUV observations are being used to find and study these populations.Comment: 15 pages, 6 figures; invited "Brief Review" for Modern Physics Letters

A single amino acid switch converts the sleeping beauty transposase into an efficient unidirectional excisionase with utility in stem cell reprogramming

The Sleeping Beauty (SB) transposon is an advanced tool for genetic engineering and a useful model to investigate cut-and-paste DNA transposition in vertebrate cells. Here, we identify novel SB transposase mutants that display efficient and canonical excision but practically unmeasurable genomic re-integration. Based on phylogenetic analyses, we establish compensating amino acid replacements that fully rescue the integration defect of these mutants, suggesting epistasis between these amino acid residues. We further show that the transposons excised by the exc(+)/int(-) transposase mutants form extrachromosomal circles that cannot undergo a further round of transposition, thereby representing dead-end products of the excision reaction. Finally, we demonstrate the utility of the exc(+)/int(-) transposase in cassette removal for the generation of reprogramming factor-free induced pluripotent stem cells. Lack of genomic integration and formation of transposon circles following excision is reminiscent of signal sequence removal during V(D)J recombination, and implies that cut-and-paste DNA transposition can be converted to a unidirectional process by a single amino acid change

Molecular and functional characterization of BDNF-overexpressing human retinal pigment epithelial cells established by sleeping beauty transposon-mediated gene transfer

More and more patients suffer from multifactorial neurodegenerative diseases, such as age-related macular degeneration (AMD). However, their pathological mechanisms are still poorly understood, which complicates the development of effective therapies. To improve treatment of multifactorial diseases, cell-based gene therapy can be used to increase the expression of therapeutic factors. To date, there is no approved therapy for dry AMD, including late-stage geographic atrophy. We present a treatment option for dry AMD that transfers the brain-derived neurotrophic factor (BDNF) gene into retinal pigment epithelial (RPE) cells by electroporation using the plasmid-based Sleeping Beauty (SB) transposon system. ARPE-19 cells and primary human RPE cells were co-transfected with two plasmids encoding the (SB100X) transposase and the transposon carrying a BDNF transcription cassette. We demonstrated efficient expression and secretion of BDNF in both RPE cell types, which were further increased in ARPE-19 cell cultures exposed to hydrogen peroxide. BDNF-transfected cells exhibited lower apoptosis rates and stimulated neurite outgrowth in human SH-SY5Y cells. This study is an important step in the development of a cell-based BDNF gene therapy that could be applied as an advanced therapy medicinal product to treat dry AMD or other degenerative retinal diseases

CO Isotopes in Planetary Nebulae

Standard stellar evolution theory is inconsistent with the observed isotopic carbon ratio, 12C/13C, in evolved stars. This theory is also inconsistent with the 3He/H abundance ratios observed in Galactic HII regions, when combined with chemical evolution theory. These discrepancies have been attributed to an extra, non-standard mixing which further processes material during the RGB and should lower both the 12C/13C and 3He/H abundance ratios for stars with masses < 2 solar masses. Measurements of isotopic ratios in planetary nebulae probe material which escapes the star to be further processed by future generations of stars. We have measured the carbon isotopic abundance ratio, 12C/13C, in 11 planetary nebulae (PNe) by observing the J=2-->1 and J=3-->2 millimeter transitions of 12CO and 13CO in molecular clouds associated with the PNe. A large velocity gradient (LVG) model has been used to determine the physical conditions for each PNe where both transitions have been detected. We detect both 12CO and 13CO in 9 PNe. If 12CO/13CO = 12C/13C, the range of 12C/13C is 2.2--31. Our results support theories which include some form of extra mixing.Comment: 23 pages including 3 figures; accepted for publication in the Ap

The SET and transposase domain protein Metnase enhances chromosome decatenation: regulation by automethylation

Metnase is a human SET and transposase domain protein that methylates histone H3 and promotes DNA double-strand break repair. We now show that Metnase physically interacts and co-localizes with Topoisomerase IIα (Topo IIα), the key chromosome decatenating enzyme. Metnase promotes progression through decatenation and increases resistance to the Topo IIα inhibitors ICRF-193 and VP-16. Purified Metnase greatly enhanced Topo IIα decatenation of kinetoplast DNA to relaxed circular forms. Nuclear extracts containing Metnase decatenated kDNA more rapidly than those without Metnase, and neutralizing anti-sera against Metnase reversed that enhancement of decatenation. Metnase automethylates at K485, and the presence of a methyl donor blocked the enhancement of Topo IIα decatenation by Metnase, implying an internal regulatory inhibition. Thus, Metnase enhances Topo IIα decatenation, and this activity is repressed by automethylation. These results suggest that cancer cells could subvert Metnase to mediate clinically relevant resistance to Topo IIα inhibitors

Hsmar1 transposition is sensitive to the topology of the transposon donor and the target

Hsmar1 is a member of the Tc1-mariner superfamily of DNA transposons. These elements mobilize within the genome of their host by a cut-and-paste mechanism. We have exploited the in vitro reaction provided by Hsmar1 to investigate the effect of DNA supercoiling on transposon integration. We found that the topology of both the transposon and the target affect integration. Relaxed transposons have an integration defect that can be partially restored in the presence of elevated levels of negatively supercoiled target DNA. Negatively supercoiled DNA is a better target than nicked or positively supercoiled DNA, suggesting that underwinding of the DNA helix promotes target interactions. Like other Tc1-mariner elements, Hsmar1 integrates into 5′-TA dinucleotides. The direct vicinity of the target TA provides little sequence specificity for target interactions. However, transposition within a plasmid substrate was not random and some TA dinucleotides were targeted preferentially. The distribution of intramolecular target sites was not affected by DNA topology