635 research outputs found
Emission from Water Vapor and Absorption from Other Gases at 5-7.5 Microns in Spitzer-IRS Spectra of Protoplanetary Disks
We present spectra of 13 T Tauri stars in the Taurus-Auriga star-forming
region showing emission in Spitzer Space Telescope Infrared Spectrograph (IRS)
5-7.5 micron spectra from water vapor and absorption from other gases in these
stars' protoplanetary disks. Seven stars' spectra show an emission feature at
6.6 microns due to the nu_2 = 1-0 bending mode of water vapor, with the shape
of the spectrum suggesting water vapor temperatures > 500 K, though some of
these spectra also show indications of an absorption band, likely from another
molecule. This water vapor emission contrasts with the absorption from warm
water vapor seen in the spectrum of the FU Orionis star V1057 Cyg. The other
six of the thirteen stars have spectra showing a strong absorption band,
peaking in strength at 5.6-5.7 microns, which for some is consistent with
gaseous formaldehyde (H2CO) and for others is consistent with gaseous formic
acid (HCOOH). There are indications that some of these six stars may also have
weak water vapor emission. Modeling of these stars' spectra suggests these
gases are present in the inner few AU of their host disks, consistent with
recent studies of infrared spectra showing gas in protoplanetary disks.Comment: 33 pages, 9 figures, to appear in the 20 August, 2014, V791 - 2 issue
of the Astrophysical Journa
Millimeter imaging of HD 163296: probing the disk structure and kinematics
We present new multi-wavelength millimeter interferometric observations of
the Herbig Ae star HD 163296 obtained with the IRAM/PBI, SMA and VLA arrays
both in continuum and in the 12CO, 13CO and C18O emission lines. Gas and dust
properties have been obtained comparing the observations with self-consistent
disk models for the dust and CO emission. The circumstellar disk is resolved
both in the continuum and in CO. We find strong evidence that the circumstellar
material is in Keplerian rotation around a central star of 2.6 Msun. The disk
inclination with respect to the line of sight is 46+-4 deg with a position
angle of 128+-4 deg. The slope of the dust opacity measured between 0.87 and 7
mm (beta=1) confirms the presence of mm/cm-size grains in the disk midplane.
The dust continuum emission is asymmetric and confined inside a radius of 200
AU while the CO emission extends up to 540 AU. The comparison between dust and
CO temperature indicates that CO is present only in the disk interior. Finally,
we obtain an increasing depletion of CO isotopomers from 12CO to 13CO and C18O.
We argue that these results support the idea that the disk of HD 163296 is
strongly evolved. In particular, we suggest that there is a strong depletion of
dust relative to gas outside 200 AU; this may be due to the inward migration of
large bodies that form in the outer disk or to clearing of a large gap in the
dust distribution by a low mass companion.Comment: Accepted for publication on A&A, 16 page
Analysis of Lipid-linked Oligosaccharides Synthesized in vivo in Schizosaccharomyces pombe
Dolichol diphosphate-linked oligosaccharides (LLO) are the sugar donors in N-glycosylation, a fundamental protein post-translational modification of the eukaryotic secretory pathway. Defects in LLO biosynthesis produce human Congenital Disorders of Glycosylation Type I. The synthesis of LLOs and the transfer reactions to their protein acceptors is highly conserved among animal, plant, and fungi kingdoms, making the fission yeast Schizosaccharomyces pombe a suitable model to study these processes. Here, we present a protocol to determine the LLO patterns produced in vivo by S. pombe cells that may be easily adapted to other cell types. First, exponentially growing cultures are labeled with a pulse of [14C]-glucose. LLOs are then purified by successive extractions with organic solvents, and glycans are separated from the lipid moieties in mild acid hydrolysis and a new solvent extraction. The purified glycans are then run on paper chromatography. We use a deconvolution process to adjust the profile obtained to the minimal number of Gaussian functions needed to fit the data and determine the proportion of each species with respect to total glycan species present in the cell. The method we provide here might be used without any expensive or specialized equipment. The deconvolution process described here might also be useful to analyze species in non-completely resolved chromatograms.Fil: Valko, AyelĂ©n. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Instituto de Investigaciones BioquĂmicas de Buenos Aires. FundaciĂłn Instituto Leloir. Instituto de Investigaciones BioquĂmicas de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, BiotecnologĂa y BiologĂa Traslacional; ArgentinaFil: Gallo, Giovanna Lucrecia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, BiotecnologĂa y BiologĂa Traslacional; Argentina. Ministerio de ProducciĂłn y Trabajo. SecretarĂa de Gobierno de Agroindustria. Servicio Nacional de Sanidad y Calidad Agroalimentaria. Centro de VirologĂa Humana y Animal. - Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Centro de VirologĂa Humana y Animal; ArgentinaFil: Weisz, Ariel D.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, BiotecnologĂa y BiologĂa Traslacional; ArgentinaFil: Parodi, Armando JosĂ© A.. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Instituto de Investigaciones BioquĂmicas de Buenos Aires. FundaciĂłn Instituto Leloir. Instituto de Investigaciones BioquĂmicas de Buenos Aires; ArgentinaFil: D'alessio, Cecilia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, BiotecnologĂa y BiologĂa Traslacional; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Engineered Sleeping Beauty Transposon as Efficient System to Optimize Chimp Adenoviral Production
Sleeping Beauty (SB) is the first DNA transposon employed for efficient transposition in vertebrate cells, opening new applications for genetic engineering and gene therapies. A transposon-based gene delivery system holds the favourable features of non-viral vectors and an attractive safety profile. Here, we employed SB to engineer HEK293 cells for optimizing the production of a chimpanzee Adenovector (chAd) belonging to the Human Mastadenovirus C species. To date, chAd vectors are employed in several clinical settings for infectious diseases, last but not least COVID-19. A robust, efficient and quick viral vector production could advance the clinical application of chAd vectors. To this aim, we firstly swapped the hAd5 E1 with chAd-C E1 gene by using the CRISPR/Cas9 system. We demonstrated that in the absence of human Ad5 E1, chimp Ad-C E1 gene did not support HEK293 survival. To improve chAd-C vector production, we engineered HEK293 cells to stably express the chAd-C precursor terminal protein (ch.pTP), which plays a crucial role in chimpanzee Adenoviral DNA replication. The results indicate that exogenous ch.pTP expression significantly ameliorate the packaging and amplification of recombinant chAd-C vectors thus, the engineered HEK293ch.pTP cells could represent a superior packaging cell line for the production of these vectors
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The Spitzer Infrared Spectrograph Survey of T Tauri Stars in Taurus
We present 161 Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars and young brown dwarfs in the Taurus star-forming region. All of the targets were selected based on their infrared excess and are therefore surrounded by protoplanetary disks; they form the complete sample of all available IRS spectra of T Tauri stars with infrared excesses in Taurus. We also present the IRS spectra of seven Class 0/I objects in Taurus to complete the sample of available IRS spectra of protostars in Taurus. We use spectral indices that are not significantly affected by extinction to distinguish between envelope-and disk-dominated objects. Together with data from the literature, we construct spectral energy distributions for all objects in our sample. With spectral indices derived from the IRS spectra we infer disk properties such as dust settling and the presence of inner disk holes and gaps. We find a transitional disk frequency, which is based on objects with unusually large 13-31 mu m spectral indices indicative of a wall surrounding an inner disk hole, of about 3%, and a frequency of about 20% for objects with unusually large 10 mu m features, which could indicate disk gaps. The shape and strength of the 10 mu m silicate emission feature suggests weaker 10 mu m emission and more processed dust for very low mass objects and brown dwarfs (spectral types M6-M9). These objects also display weaker infrared excess emission from their disks, but do not appear to have more settled disks than their higher-mass counterparts. We find no difference for the spectral indices and properties of the dust between single and multiple systems.NASANASA through JPL/CaltechNASA through the Spitzer Space TelescopeNational Science Foundation AST-0544588, 0901947Pennsylvania State UniversityEberly College of SciencePennsylvania Space Grant ConsortiumNSFAstronom
Rotational Line Emission from Water in Protoplanetary Disks
Circumstellar disks provide the material reservoir for the growth of young
stars and for planet formation. We combine a high-level radiative transfer
program with a thermal-chemical model of a typical T Tauri star disk to
investigate the diagnostic potential of the far-infrared lines of water for
probing disk structure. We discuss the observability of pure rotational H2O
lines with the Herschel Space Observatory, specifically the residual gas where
water is mainly frozen out. We find that measuring both the line profile of the
ground 110-101 ortho-H2O transition and the ratio of this line to the 312-303
and 221-212 line can provide information on the gas phase water between 5-100
AU, but not on the snow line which is expected to occur at smaller radii.Comment: 5 pages, 4 figures. Accepted by ApJ
Impact of grain evolution on the chemical structure of protoplanetary disks
We study the impact of dust evolution in a protoplanetary disk around a T
Tauri star on the disk chemical composition. For the first time we utilize a
comprehensive model of dust evolution which includes growth, fragmentation and
sedimentation. Specific attention is paid to the influence of grain evolution
on the penetration of the UV field in the disk. A chemical model that includes
a comprehensive set of gas phase and grain surface chemical reactions is used
to simulate the chemical structure of the disk. The main effect of the grain
evolution on the disk chemical composition comes from sedimentation, and, to a
lesser degree, from the reduction of the total grain surface area. The net
effect of grain growth is suppressed by the fragmentation process which
maintains a population of small grains, dominating the total grain surface
area. We consider three models of dust properties. In model GS both growth and
sedimentation are taken into account. In models A5 and A4 all grains are
assumed to have the same size (10(-5) cm and 10(-4) cm, respectively) with
constant gas-to-dust mass ratio of 100. Like in previous studies, the
"three-layer" pattern (midplane, molecular layer, hot atmosphere) in the disk
chemical structure is preserved in all models, but shifted closer to the
midplane in models with increased grain size (GS and A4). Unlike other similar
studies, we find that in models GS and A4 column densities of most gas-phase
species are enhanced by 1-3 orders of magnitude relative to those in a model
with pristine dust (A5), while column densities of their surface counterparts
are decreased. We show that column densities of certain species, like C2H,
HC(2n+1)N (n=0-3), H2O and some other molecules, as well as the C2H2/HCN
abundance ratio which are accessible with Herschel and ALMA can be used as
observational tracers of early stages of the grain evolution process in
protoplanetary disks.Comment: 50 pages, 4 tables, 11 figures, accepted to the Ap
The Structure of the DoAr 25 Circumstellar Disk
We present high spatial resolution (< 0.3" = 40\Sigma
\propto r^{-p}$ with p = 0.34, significantly less steep than a steady-state
accretion disk (p = 1) or the often adopted minimum mass solar nebula (p =
1.5). Even though the total mass of material is large (M_d = 0.10 M_sun), the
densities inferred in the inner disk for such a model may be too low to
facilitate any mode of planet formation. However, alternative models with
steeper density gradients (p = 1) can explain the observations equally well if
substantial grain growth in the planet formation region (r < 40 AU) has
occurred. We discuss these data in the context of such models with dust
properties that vary with radius and highlight their implications for
understanding disk evolution and the early stages of planet formation.Comment: ApJL in pres
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