187 research outputs found
Spectrophotometry of HII Regions, Diffuse Ionized Gas and Supernova Remnants in M31: The Transition from Photo- to Shock-Ionization
We present results of KPNO 4-m optical spectroscopy of discrete emission-line
nebulae and regions of diffuse ionized gas (DIG) in M31. Long-slit spectra of
16 positions in the NE half of M31 were obtained over a 5-15 kpc range in
radial distance from the center of the galaxy. The spectra have been used to
confirm 16 supernova remnant candidates from the Braun & Walterbos (1993)
catalog. The slits also covered 46 HII regions which show significant
differences among the various morphological types (center-brightened, diffuse,
rings). Radial gradients in emission-line ratios such as [OIII]/H and
[OII]/[OIII] are observed most prominently in the center-brightened HII
regions. These line ratio trends are either much weaker or completely absent in
the diffuse and ring nebulae. The line ratio gradients previously seen in M31
SNRs (Blair, Kirshner, & Chevalier 1981; 1982) are well reproduced by our new
data. The spectra of center-brightened HII regions and SNRs confirm previous
determinations of the radial abundance gradient in M31. We use diagnostic
diagrams which separate photoionized gas from shock-ionized gas to compare the
spectral properties of HII regions, SNRs and DIG. This analysis strengthens
earlier claims (Greenawalt, Walterbos, & Braun 1997) that the DIG in the disk
of M31 is photoionized by a dilute radiation field.Comment: 45 pages, 9 figures, 7 tables, to appear in the Astronomical Journal
(December 1999
The Resolved Narrow Line Region in NGC4151
We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from
the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the
kinematics and physical conditions of the emission line clouds in this region.
Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and
narrow band undispersed images, we have mapped the NLR velocity field from 1.2
kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud
distribution exhibits recessional velocities relative to the nucleus to the NE
and approaching velocities to the SW of the nucleus. We find evidence for at
least two kinematic components in the NLR. One kinematic component is
characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v|
< 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR
and their observed kinematics may be gravitationally associated with the host
galaxy. Another component is characterized by High Velocities and High Velocity
Dispersions (HVHVD clouds: 400 130 km/s). This
set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has
radial velocities which are too high to be gravitational in origin, but show no
strong correlation between velocity or velocity dispersion and the position of
the radio knots. Outflow scenarios will be discussed as the driving mechanism
for these HVHVD clouds.Comment: 38 pages, 14 figures, accepted by ApJ. For higher resolution images
see http://www.pha.jhu.edu/~kaiser
Discovery of a nuclear gas bar feeding the active nucleus in Circinus
We report the discovery of gas inflow motions towards the active nucleus of
the Circinus galaxy caused by the non-axisymmetric potential of a nuclear gas
bar. Evidence for dust associated with the bar comes from the HST/NICMOS H-K
color map, whereas the streaming motions along the gas bar are seen in the
velocity field of the H2 S(1)(1-0) emission line. The gas bar is about 100 pc
long with a visual extinction in excess of 10 mag. Indication for the gaseous
nature of this bar comes from the lack of a stellar counterpart even in the K
band where the extinction is greatly reduced.
We also use the NICMOS emission line images (Pa-alpha, [SiVI], and [FeII]) to
study the innermost region of the ionization cones and the nuclear star forming
activity. We discuss the possible relationship of these components with the
gaseous bar.Comment: 14 pages, 7 figures (3 color plates), accepted for publication in Ap
Investigating The Possible Anomaly Between Nebular and Stellar Oxygen Abundances in the Dwarf Irregular Galaxy WLM
We obtained new optical spectra of 13 H II regions in WLM with EFOSC2; oxygen
abundances are derived for nine H II regions. The temperature-sensitive [O III]
4363 emission line was measured in two bright H II regions HM7 and HM9. The
direct oxygen abundances for HM7 and HM9 are 12+log(O/H) = 7.72 +/- 0.04 and
7.91 +/- 0.04, respectively. We adopt a mean oxygen abundance of 12+log(O/H) =
7.83 +/- 0.06. This corresponds to [O/H] = -0.83 dex, or 15% of the solar
value. In H II regions where [O III] 4363 was not measured, oxygen abundances
derived with bright-line methods are in general agreement with direct values of
the oxygen abundance to an accuracy of about 0.2 dex. In general, the present
measurements show that the H II region oxygen abundances agree with previous
values in the literature. The nebular oxygen abundances are marginally
consistent with the mean stellar magnesium abundance ([Mg/H] = -0.62). However,
there is still a 0.62 dex discrepancy in oxygen abundance between the nebular
result and the A-type supergiant star WLM15 ([O/H] = -0.21). Non-zero reddening
values derived from Balmer line ratios were found in H II regions near a second
H I peak. There may be a connection between the location of the second H I
peak, regions of higher extinction, and the position of WLM15 on the eastern
side of the galaxy.Comment: Accepted, Ap.J.; 19 pages (AASTeX 5.2) with 6 figures. Full paper
with color figures at http://www.astro.umn.edu/~hlee
The He II Emitting Nebula N44C in the LMC: Optical/UV Spectroscopy of the Nebula and its Ionizing Star
We present HST spectroscopy and imaging, along with new ground-based
spectroscopy and ROSAT HRI imaging, of the He II emitting nebula N44C and its
ionizing star. A GHRS spectrogram of the ionizing star yields a spectral type
of about O7 for the star. The lack of P Cygni profiles for Si IV and C IV
indicates that the star is not a supergiant. The nebular abundances in the
ionized gas are consistent with average abundances for LMC H II regions, with
the possible exception that nitrogen may be enhanced. Enrichment by a former
evolved companion star is not evident. A long-slit echelle spectrogram in
H-alpha + [N II] shows no evidence for high-velocity gas in N44C. This rules
out high-velocity shocks as the source of the nebular He II emission. A 108 ks
ROSAT HRI image of N44C shows no X-ray point source to a 3-sigma upper limit
L(X) < 10^34 erg s^-1 in the 0.1-2.0 keV band. Based on new measurements of the
electron density in the He II emitting region, we derive recombination
timescales of approximately 20 yrs for He^+2 and approximately 4 yrs for Ne^+4.
If N44C is a fossil X-ray ionized nebula, this places severe constraints on
when the putative X-ray source could have turned off. The presence of strong
[Ne IV] emission in the nebula is puzzling if the ionizing source has turned
off. It is possible the system is related to the Be X-ray binaries, although
the O star in N44C does not show Be characteristics at the present time.
Monitoring of X-rays and He II emission from the nebula, as well as a radial
velocity study of the ionizing star, are needed to fully understand the
emission line spectrum of N44C.Comment: 37 pages, 7 figures (1 color .gif image); accepted for publication in
the 10 Dec 2000 Astrophysical Journal. Complete PostScript and PDF versions
can also be obtained at http://ocotillo.as.arizona.edu/~dgarnet
BIOSYNTHESIS OF PHOSPHATIDYLINOSITOL *
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73945/1/j.1749-6632.1970.tb56440.x.pd
Carcinoembryonic Antigen Gene Family
The carcinoembryonic antigen (CEA) gene family belongs to the immunoglobulin supergene family and can be divided into two main subgroups based on sequence comparisons. In humans it is clustered on the long arm of chromosome 19 and consists of approximately 20 genes. The CEA subgroup genes code for CEA and its classical crossreacting antigens, which are mainly membrane-bound, whereas the other subgroup genes encode the pregnancy-specific glycoproteins (PSG), which are secreted. Splice variants of individual genes and differential post-translational modifications of the resulting proteins, e.g., by glycosylation, indicate a high complexity in the number of putative CEA-related molecules. So far, only a limited number of CEA-related antigens in humans have been unequivocally assigned to a specific gene. Rodent CEA-related genes reveal a high sequence divergence and, in part, a completely different domain organization than the human CEA gene family, making it difficult to determine individual gene counterparts. However, rodent CEA-related genes can be assigned to human subgroups based on similarity of expression patterns, which is characteristic for the subgroups. Various functions have been determined for members of the CEA subgroup in vitro, including cell adhesion, bacterial binding, an accessory role for collagen binding or ecto-ATPases activity. Based on all that is known so far on its biology, the clinical outlook for the CEA family has been reassessed
Roles of Major Facilitator Superfamily Transporters in Phosphate Response in Drosophila
The major facilitator superfamily (MFS) transporter Pho84 and the type III transporter Pho89 are responsible for metabolic effects of inorganic phosphate in yeast. While the Pho89 ortholog Pit1 was also shown to be involved in phosphate-activated MAPK in mammalian cells, it is currently unknown, whether orthologs of Pho84 have a role in phosphate-sensing in metazoan species. We show here that the activation of MAPK by phosphate observed in mammals is conserved in Drosophila cells, and used this assay to characterize the roles of putative phosphate transporters. Surprisingly, while we found that RNAi-mediated knockdown of the fly Pho89 ortholog dPit had little effect on the activation of MAPK in Drosophila S2R+ cells by phosphate, two Pho84/SLC17A1β9 MFS orthologs (MFS10 and MFS13) specifically inhibited this response. Further, using a Xenopus oocyte assay, we show that MSF13 mediates uptake of [Β³Β³P]-orthophosphate in a sodium-dependent fashion. Consistent with a role in phosphate physiology, MSF13 is expressed highest in the Drosophila crop, midgut, Malpighian tubule, and hindgut. Altogether, our findings provide the first evidence that Pho84 orthologs mediate cellular effects of phosphate in metazoan cells. Finally, while phosphate is essential for Drosophila larval development, loss of MFS13 activity is compatible with viability indicating redundancy at the levels of the transporters.National Institutes of Health (U.S.) (NIDDK 5K08DK078361)Harvard Catalys
Intraspecific Aflatoxin Inhibition in Aspergillus flavus Is Thigmoregulated, Independent of Vegetative Compatibility Group and Is Strain Dependent
Biological control of preharvest aflatoxin contamination by atoxigenic stains of Aspergillus flavus has been demonstrated in several crops. The assumption is that some form of competition suppresses the fungus's ability to infect or produce aflatoxin when challenged. Intraspecific aflatoxin inhibition was demonstrated by others. This work investigates the mechanistic basis of that phenomenon. A toxigenic and atoxigenic isolate of A. flavus which exhibited intraspecific aflatoxin inhibition when grown together in suspended disc culture were not inhibited when grown in a filter insert-plate well system separated by a .4 or 3 Β΅m membrane. Toxigenic and atoxigenic conidial mixtures (50βΆ50) placed on both sides of these filters restored inhibition. There was βΌ50% inhibition when a 12 Β΅m pore size filter was used. Conidial and mycelial diameters were in the 3.5β7.0 Β΅m range and could pass through the 12 Β΅m filter. Larger pore sizes in the initially separated system restored aflatoxin inhibition. This suggests isolates must come into physical contact with one another. This negates a role for nutrient competition or for soluble diffusible signals or antibiotics in aflatoxin inhibition. The toxigenic isolate was maximally sensitive to inhibition during the first 24 hrs of growth while the atoxigenic isolate was always inhibition competent. The atoxigenic isolate when grown with a green fluorescent protein (GFP) toxigenic isolate failed to inhibit aflatoxin indicating that there is specificity in the touch inhibiton. Several atoxigenic isolates were found which inhibited the GFP isolate. These results suggest that an unknown signaling pathway is initiated in the toxigenic isolate by physical interaction with an appropriate atoxigenic isolate in the first 24 hrs which prevents or down-regulates normal expression of aflatoxin after 3β5 days growth. We suspect thigmo-downregulation of aflatoxin synthesis is the mechanistic basis of intraspecific aflatoxin inhibition and the major contributor to biological control of aflatoxin contamination
- β¦