24 research outputs found
Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss
We searched for a correlation between the two anomalous properties of K
giants: Li enhancement and IR excess from an unbiased survey of a large sample
of RGB stars. A sample of 2000 low-mass K giants with accurate astrometry from
the Hipparcos catalog was chosen for which Li abundances have been determined
from low-resolution spectra. Far-infrared data were collected from the
and catalogs. To probe the correlation between the two anomalies, we
supplemented 15 Li-rich K giants discovered from this sample with 25 known
Li-rich K giants from other studies. Dust shell evolutionary models and
spectral energy distributions were constructed using the code DUSTY to estimate
different dust shell properties, such as dust evolutionary time scales, dust
temperatures, and mass-loss rates. Among 2000 K giants, we found about two
dozen K giants with detectable far-IR excess, and surprisingly, none of them
are Li-rich. Similarly, the 15 new Li-rich K giants that were identified from
the same sample show no evidence of IR excess. Of the total 40 Li-rich K
giants, only 7 show IR excess. Important is that K giants with Li enhancement
and/or IR excess begin to appear only at the bump on the RGB. Results show that
K giants with IR excess are very rare, similar to K giants with Li enhancement.
This may be due to the rapid differential evolution of dust shell and Li
depletion compared to RGB evolutionary time scales. We also infer from the
results that during the bump evolution, giants probably undergo some internal
changes, which are perhaps the cause of mass-loss and Li-enhancement events.
However, the available observational results do not ascertain that these
properties are correlated. That a few Li-rich giants have IR excess seems to be
pure coincidence.Comment: Accepted for Publication in Astronomy & Astrophysics, 6 figures, 5
tables, 19 page
Subarcsecond mid-infrared imaging of dust in the bipolar nebula Hen 3-401
We present high-resolution, nearly diffraction-limited narrow- and broadband mid-IR images of bipolar reflection nebula Hen 3-401. The deconvolved images yield a pixel-limited spatial resolution of 0″.09, demonstrating the superior imaging quality of the Gemini telescope. The infrared image of Hen 3-401 consists of a prominent core region of size 1″ and extended emissions along the walls of the bipolar lobes. We find that the distribution of aromatic infrared band (AIB) emission is different from that of the continuum emission and that the star has undergone multiple ejection of the AIB emission feature carrier at the end stages of its evolution. From the observed temperature gradient in the core, we suggest that the core has a flared disk geometry. © 2006. The American Astronomical Society. All rights reserved.published_or_final_versio
2D Monte-Carlo Radiative transfer modeling of the disk shaped secondary of Epsilon Aurigae
We present two dimensional Monte-Carlo radiative transfer models for the disk
of the eclipsing binary Aur by fitting its spectral energy
distribution from optical to the far-IR wavelengths. We also report new
observations of Aur made by AKARI in its five mid and far-IR
photometric bands and were used to construct our SED. The disk is optically
thick and has flared disk geometry containing gas and dust with a gas to dust
mass ratio of 100. We have taken the primary of the binary to be a F0Iae-type
post-AGB star and the disk is heated by a B5V hot star with a temperature of
15,000 K at the center of the disk. We take the radius of the disk to be 3.8 AU
for our models as constrained from the IR interferometric imaging observations
of the eclipsing disk. Our models imply that the disk contains grains which are
much bigger than the ISM grains (grain sizes 10 to 100). The grain
chemistry of the disk is carbonaceous and our models show that silicate and ISM
dust chemistry do not reproduce the slope of the observed SED in the mid-IR to
far-IR regions. This implies that the formation of the disk shaped secondary in
Aur system could be the result of accretion of matter and or mass
transfer from the primary which is now a F0Iae post-AGB star. It is not a
proto-planetary disk. The disk is seen nearly edge on with an inclination angle
larger than 85. We propose from our radiative transfer modeling that the
disk is not solid and have a void of 2AU radius at the center within which no
grains are present making the region nearly transparent. The disk is not
massive, its mass is derived to be less than 0.005M.Comment: 27 pages, 5 figures, 2 table
Sub-arcsec mid-IR imaging of OH 231.8+4.2
We present 0.18″ resolution mid-infrared images of OH231.8+4.2 using the Gemini South telescope. The images show a, bright central core of ∼1″ in size, with extended emissions in the lobes. We find evidence for different chemical composition of the dust in the core and the lobes from the narrow-band images. © 2006 International Astronomical Union.link_to_subscribed_fulltex
Molecular hydrogen jets, filaments, and haloes in planetary nebulae
We present deep H2 images of planetary nebulae obtained with the CHFTIR camera of the Canada-France-Hawaii Telescope. Molecular hydrogen emissions are seen in the equatorial torus, bipolar lobes, as well as in extended haloes. Radial equatorial jets are also detected in a number of bipolar nebulae. © 2006 International Astronomical Union.link_to_subscribed_fulltex
Probing infrared excess connection with Li enhancement among red clump giants
We have performed a search among low mass red giants for finding evidence for
merger scenario for triggering He-flash and subsequent Li enhancement. We chose
a sample of red giants from GALAH survey with well-measured Li abundances, and
near and mid-IR fluxes from 2MASS and WISE surveys, respectively. The sample
contains 418 cool red clump giants and 359 upper red giant branch giants. Most
of the giants and majority of super Li-rich giants show no IR excess. Only five
red clump giants and one RGB giant show IR excess. Notably, of the five red
clump giants with IR excess, three are super Li-rich (A(Li) > = 3.2 dex), and
two are Li-rich (A(Li) > = 1.0 dex). Results suggest Li enhancement among red
clump giants may be due to two channels: one resulting from in-situ He-flash in
single star evolution and the other due to He-flash triggered by events like
merger of He-white dwarfs with giants He-inert core on RGB. In the latter case,
IR excess, as a result of mass loss, is expected from merger events. We have
modelled IR excess in all six giants using DUSTY code and derived dust
parameters. The estimated kinematic ages and time scales of dust envelopes of
the super Li-rich phase suggest Li enhancement took place very recently.
Further, the analysis shows a significantly higher proportion (four out of five
red clump giants) of rapid rotators (vsini > = 8 km/s) among Li-rich giants
with IR excess compared to Li-normal and Li-rich giants with no IR excess.Comment: 11 pages, 7 figures, 5 table