490 research outputs found
Antibacterial Activity of Some Indian Medicinal Plants
The preliminary phytochemical study and in vitro antibacterial activity of the ethanolic extracts of three plants having ethnomedicinal uses collected from tribal belt of Orissa, India, viz. Litsea glutinosa L.: Lauraceae (LG), Vitex peduncularis W.: Verbenaceae (VP), Elephantopus scaber L.: Asteraceae (ES) were investigated. The preliminary phytochemical analysis of the extracts revealed the presence of carbohydrate, tannin, alkaloid in LG, tannin, flavonoid, saponin, alkaloid in VP and flavonoid, saponin, steroid, alkaloid, glycoside in ES. The extracts were subjected for screening of in vitro antibacterial activity against selected major urinary tract infection (UTI) causing pathogens viz. Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis and Escherichia coli at the concentrations of 500 and 250 µg/ml by disc diffusion assay method. The results of antibacterial activity revealed that all the extract showed good inhibitory activity against all the tested pathogens and the ES extract showed comparative by better activity than the other extracts. The activity of the extract were compared with standard antibiotics
Long-term evolution of FU Orionis objects at infrared wavelengths
We investigate the brightness evolution of 7 FU Orionis systems in the 1-100
micrometer wavelength range using data from the Infrared Space Observatory
(ISO). The ISO measurements were supplemented with 2MASS and MSX observations
performed in the same years as the ISO mission (1995-98). The spectral energy
distributions (SEDs) based on these data points were compared with earlier ones
derived from the IRAS photometry as well as from ground-based observations
carried out around the epoch 1983. In 3 cases (Z CMa, Parsamian 21, V1331 Cyg)
no difference between the two epochs was seen within the measurement
uncertainties. V1057 Cyg, V1515 Cyg and V1735 Cyg have become fainter at
near-infrared wavelengths while V346 Nor has become slightly brighter. V1057
Cyg exhibits a similar flux change also in the mid-infrared. At lambda >= 60
micrometer most of the sources remained constant; only V346 Nor seems to fade.
Our data on the long-term evolution of V1057 Cyg agree with the model
predictions of Kenyon & Hartmann (1991) and Turner et al. (1997) at near- and
mid-infrared wavelengths, but disagree at lambda > 25 micrometer. We discuss if
this observational result at far-infrared wavelengths could be understood in
the framework of the existing models.Comment: 9 pages, 3 figures, to be published in Astronomy & Astrophysic
Ethnobotanical Exploration of Malkangiri District of Orissa, India
The association of man with the neighborhood flora starts with human civilization. Besides food, feed clothes and shelter, plants are important source of drugs. These plants or its parts therefore used either directly or after processing by the native people against various diseases, disorders and ailments. A survey was conducted on the tribal district of Malkangiri of Orissa to identify and record various ethno medicinally important plants and their medicinal uses. In the present investigation there are 134 species of plants belong to 69 families and 128 genera are recorded and used in various ailments by different tribes of Malkangiri district of Orissa
Quiescent H2 Emission From Pre-Main Sequence Stars in Chamaeleon I
We report the discovery of quiescent emission from molecular hydrogen gas
located in the circumstellar disks of six pre-main sequence stars, including
two weak-line T Tauri stars (TTS), and one Herbig AeBe star, in the Chamaeleon
I star forming region. For two of these stars, we also place upper limits on
the 2->1 S(1)/1->0 S(1) line ratios of 0.4 and 0.5. Of the 11 pre-main sequence
sources now known to be sources of quiescent near-infrared hydrogen emission,
four possess transitional disks, which suggests that detectable levels of H
emission and the presence of inner disk holes are correlated. These H
detections demonstrate that these inner holes are not completely devoid of gas,
in agreement with the presence of observable accretion signatures for all four
of these stars and the recent detections of [Ne II] emission from three of
them. The overlap in [Ne II] and H detections hints at a possible
correlation between these two features and suggests a shared excitation
mechanism of high energy photons. Our models, combined with the kinematic
information from the H lines, locate the bulk of the emitting gas at a few
tens of AU from the stars. We also find a correlation between H detections
and those targets which possess the largest H equivalent widths,
suggesting a link between accretion activity and quiescent H emission. We
conclude that quiescent H emission from relatively hot gas within the disks
of TTS is most likely related to on-going accretion activity, the production of
UV photons and/or X-rays, and the evolutionary status of the dust grain
populations in the inner disks.Comment: 12 pages, emulateapj, Accepted by Ap
No Fossil Disk in the T Tauri Multiple System V773 Tau
We present new multi-epoch near-infrared and optical high-angular images of
the V773 Tau pre-main sequence triple system, a weak-line T Tauri (WTTS) system
in which the presence of an evolved, ``fossil'' protoplanetary disk has been
inferred on the basis of a significant infrared excess. Our images reveal a
fourth object bound to the system, V773 Tau D. While it is much fainter than
all other components at 2 micron, it is the brightest source in the system at
4.7 micron. We also present medium-resolution K band adaptive optics
spectroscopy of this object, which is featureless with the exception of a weak
Br gamma emission line. Based on this spectrum and on the spectral energy
distribution of the system, we show that V773 Tau D is another member of the
small class of ``infrared companions'' (IRCs) to T Tauri stars. It is the least
luminous, and probably the least massive, component of the system, as opposed
to most other IRCs, which suggests that numerous low-luminosity IRCs such as
V773 Tau D may still remain to be discovered. Furthermore, it is the source of
the strong IR excess in the system. We therefore reject the interpretation of
this excess as the signature of a fossil (or ``passive'') disk and further
suggest that these systems may be much less frequent than previously thought.
We further show that V773 Tau C is a variable classical T Tauri star (CTTS)
and that its motion provides a well constrained orbital model. We show that
V773 Tau D can be dynamically stable within this quadruple system if its orbit
is highly inclined. Finally, V773 Tau is the first multiple system to display
such a variety of evolutionary states (WTTS, CTTS, IRC), which may be the
consequence of the strong star-star interactions in this compact quadruple
system.Comment: Accepted for publication in Astrophysical Journal, 29 pages, 2
tables, 5 figure
A reconsideration of disk properties in Herbig Ae stars
This paper presents state-of-the-art spectral energy distributions (SEDs) of four Herbig Ae stars, based in part on new data in the mid and far-infrared and at millimeter wavelengths. The SEDs are discussed in the context of circumstellar disk models. We show that models of irradiated disks provide a good fit to the observations over the whole range of wavelengths. We offer a possible solution to the long-standing puzzle caused by the excess emission of Herbig Ae stars, where a large fraction of the stellar luminosity is re-radiated between ~1.25 and 7 μm, with a peak at about 3 μm. We suggest that this general behaviour can be caused by dust evaporation in disks where the gas component is optically thin to the stellar radiation, as expected if the accretion rate is very low. The creation of a puffed-up inner wall of optically thick dust at the dust sublimation radius can account for the near-infrared characteristics of the SEDs. It can also naturally explain the H and K band interferometric observations of AB Aur (Millan-Gabet et al. [CITE]), which reveal a ring of emission of radius ~0.3 AU. Finally, irradiated disk models can easily explain the observed intensity of the 10 μm silicate features and their variation from star to star
Gaia DR2 view of the Lupus V-VI clouds: the candidate diskless young stellar objects are mainly background contaminants
Extensive surveys of star-forming regions with Spitzer have revealed
populations of disk-bearing young stellar objects. These have provided crucial
constraints, such as the timescale of dispersal of protoplanetary disks,
obtained by carefully combining infrared data with spectroscopic or X-ray data.
While observations in various regions agree with the general trend of
decreasing disk fraction with age, the Lupus V and VI regions appeared to have
been at odds, having an extremely low disk fraction. Here we show, using the
recent Gaia data release 2 (DR2), that these extremely low disk fractions are
actually due to a very high contamination by background giants. Out of the 83
candidate young stellar objects (YSOs) in these clouds observed by Gaia, only
five have distances of 150 pc, similar to YSOs in the other Lupus clouds, and
have similar proper motions to other members in this star-forming complex. Of
these five targets, four have optically thick (Class II) disks. On the one
hand, this result resolves the conundrum of the puzzling low disk fraction in
these clouds, while, on the other hand, it further clarifies the need to
confirm the Spitzer selected diskless population with other tracers, especially
in regions at low galactic latitude like Lupus V and VI. The use of Gaia
astrometry is now an independent and reliable way to further assess the
membership of candidate YSOs in these, and potentially other, star-forming
regions.Comment: Accepted for publication on Astronomy&Astrophysics Letter
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