91 research outputs found
Diffraction-limited near-IR imaging at Keck reveals asymmetric, time-variable nebula around carbon star CIT 6
We present multi-epoch, diffraction-limited images of the nebula around the
carbon star CIT 6 at 2.2 microns and 3.1 microns from aperture masking on the
Keck-I telescope. The near-IR nebula is resolved into two main components, an
elongated, bright feature showing time-variable asymmetry and a fainter
component about 60 milliarcseconds away with a cooler color temperature. These
images were precisely registered (~35 milliarcseconds) with respect to recent
visible images from the Hubble Space Telescope (Trammell et al. 2000), which
showed a bipolar structure in scattered light. The dominant near-IR feature is
associated with the northern lobe of this scattering nebula, and the
multi-wavelength dataset can be understood in terms of a bipolar dust shell
around CIT 6. Variability of the near-IR morphology is qualitatively consistent
with previously observed changes in red polarization, caused by varying
illumination geometry due to non-uniform dust production. The blue emission
morphology and polarization properties can not be explained by the above model
alone, but require the presence of a wide binary companion in the vicinity of
the southern polar lobe. The physical mechanisms responsible for the breaking
of spherical symmetry around extreme carbon stars, such as CIT 6 and IRC+10216,
remain uncertain.Comment: 18 pages, 5 figures (one in color), to appear in the Astrophysical
Journa
Students’ Perceptions of Threats to their World\u27 Future: An Introduction to ICCS and Global Lesson Plan
This article explains the scope and value of the only international assessment (IEA The International Civic and Citizen Education Study, IEA ICCS) of “Civic Understanding” and a uses data from the international comparative study to create a global education lesson plan for U.S. social studies teachers to have their students consider their perceptions of threats to their world as compared to students in other countries. The lesson would most likely be used with middle and high school students
Determination of tomato quality with hyperspectral imaging
Received: February 1st, 2023 ; Accepted: July 14th, 2023 ; Published: October 13th, 2023 ; Correspondence: [email protected] (Solanum lycopersicum L.) are a widely used vegetable in the human diet
throughout the year, both fresh and in various processed products. Tomatoes contain compounds
important to human health and are an important source of vitamins, antioxidants, and mineral
elements. Performing biochemical analyses is an expensive, environmentally unfriendly and
time-consuming process; therefore, a way to determine the biochemical composition of tomatoes
using non-destructive methods is being sought. The study includes 45 varieties of tomatoes with
different colors - red, pink, orange, brown, yellow, and bicolor tomato fruits. The content of dry
matter, soluble dry matter, titratable acidity, lycopene, β-carotene, total phenol, and flavonoids
was determined by standard biochemical procedure. Reflectance spectrums of tomato fruits were
obtained with Remote Sensing Portable Spectroradiometer RS-3500 (Ltd. Spectral Evolution,
Haverhill, MA, USA) at the wavelength 350–2,500 nm with a 1 nm interval. In order to determine
the content of various biochemical parameters in tomatoes, the vegetation indices found in the
literature were used, and new ones were developed. The research demonstrated that the developed
vegetative indices allow to detect lycopene and β-carotene content non-destructively. For the
determination of the dry matter, soluble solids and phenolic content, indices designed for
detecting water content can be used, but their correlation coefficients with chemical methods are
moderately high - 0.65, 0.56 and 0.57, respectively. It was found that the best correlation between
biochemically detected parameters and vegetation indices is for lycopene > β-carotene > dry
matter> total phenols = titratable acidity ≥ soluble solids > taste index > flavonoids
Discovery of Bright Galactic R Coronae Borealis and DY Persei Variables: Rare Gems Mined from ACVS
We present the results of a machine-learning (ML) based search for new R
Coronae Borealis (RCB) stars and DY Persei-like stars (DYPers) in the Galaxy
using cataloged light curves from the All-Sky Automated Survey (ASAS) Catalog
of Variable Stars (ACVS). RCB stars - a rare class of hydrogen-deficient
carbon-rich supergiants - are of great interest owing to the insights they can
provide on the late stages of stellar evolution. DYPers are possibly the
low-temperature, low-luminosity analogs to the RCB phenomenon, though
additional examples are needed to fully establish this connection. While RCB
stars and DYPers are traditionally identified by epochs of extreme dimming that
occur without regularity, the ML search framework more fully captures the
richness and diversity of their photometric behavior. We demonstrate that our
ML method can use newly discovered RCB stars to identify additional candidates
within the same data set. Our search yields 15 candidates that we consider
likely RCB stars/DYPers: new spectroscopic observations confirm that four of
these candidates are RCB stars and four are DYPers. Our discovery of four new
DYPers increases the number of known Galactic DYPers from two to six;
noteworthy is that one of the new DYPers has a measured parallax and is m ~ 7
mag, making it the brightest known DYPer to date. Future observations of these
new DYPers should prove instrumental in establishing the RCB connection. We
consider these results, derived from a machine-learned probabilistic
classification catalog, as an important proof-of-concept for the efficient
discovery of rare sources with time-domain surveys.Comment: 18 pages, 2 new figures, accepted for publication in Ap
Faint HI 21-cm Emission Line Wings at Forbidden-Velocities
We present the results of a search for faint HI 21-cm emission line wings at
velocities forbidden by Galactic rotation in the Galactic plane using the
Leiden/Dwingeloo HI Survey data and the HI Southern Galactic Plane Survey data.
These ``forbidden-velocity wings (FVWs)'' appear as protruding excessive
emission in comparison with their surroundings in limited (< 2 deg) spatial
regions over velocity extent more than ~20 km/s in large-scale (l-v) diagrams.
Their high-velocities imply that there should be some dynamical phenomena
associated. We have identified 87 FVWs. We present their catalog, and discuss
their distribution and statistical properties. We found that 85% of FVWs are
not coincident with known supernova remnants (SNRs), galaxies, or high-velocity
clouds. Their natures are currently unknown. We suspect that many of them are
fast-moving HI shells and filaments associated with the oldest SNRs that are
essentially invisible except via their HI line emission. We discuss other
possible origins.Comment: 41 pages, 14 figures, to be published in apj
Evidence for a companion to BM Gem, a silicate carbon star
Balmer and Paschen continuum emission as well as Balmer series lines of P
Cygni-type profile from H_gamma through H_23 are revealed in the violet spectra
of BM Gem, a carbon star associated with an oxygen-rich circumstellar shell
(`silicate carbon star') observed with the high dispersion spectrograph (HDS)
on the Subaru telescope. The blue-shifted absorption in the Balmer lines
indicates the presence of an outflow, the line of sight velocity of which is at
least 400 km s^-1, which is the highest outflow velocity observed to date in a
carbon star. We argue that the observed unusual features in BM Gem are strong
evidence for the presence of a companion, which should form an accretion disk
that gives rise to both an ionized gas region and a high velocity, variable
outflow. The estimated luminosity of ~0.2 (0.03-0.6) L_sun for the ionized gas
can be maintained by a mass accretion rate to a dwarf companion of ~10^-8 M_sun
yr^-1, while ~10^-10 M_sun yr^-1 is sufficient for accretion to a white dwarf
companion. These accretion rates are feasible for some detached binary
configurations on the basis of the Bond-Hoyle type accretion process. We
concluded that the carbon star BM Gem is in a detached binary system with a
companion of low mass and low luminosity. However, we are unable to determine
whether this companion object is a dwarf or a white dwarf. The upper limits for
binary separation are 210 AU and 930 AU for a dwarf and a white dwarf,
respectively. We also note that the observed features of BM Gem mimic those of
Mira (omi Cet), which may suggest actual similarities in their binary
configurations and circumstellar structures.Comment: 11 pages, 2 figures, 1 table, accepted for publication in Ap
Tycho 2 stars with infrared excess in the MSX Point Source Catalogue
Stars of all evolutionary phases have been found to have excess infrared
emission due to the presence of circumstellar material. To identify such stars,
we have positionally correlated the infrared MSX point source catalogue and the
Tycho 2 optical catalogue. A near/mid infrared colour criteria has been
developed to select infrared excess stars. The search yielded 1938 excess
stars, over half (979) have never previously been detected by IRAS. The excess
stars were found to be young objects such as Herbig Ae/Be and Be stars, and
evolved objects such as OH/IR and carbon stars. A number of B type excess stars
were also discovered whose infrared colours could not be readily explained by
known catalogued objects.Comment: Added Comment: 16 pages, 9 figures, accepted for publication in MNRA
Sh2-205: II. Its quiescent stellar formation activity
We present a study of active stellar forming regions in the environs of the
HII region Sh2-205. The analysis is based on data obtained from point source
catalogues and images extracted from 2MASS, MSX, and IRAS surveys.
Complementary data are taken from CO survey. The identification of primary
candidates to stellar formation activity is made following colour criteria and
the correlation with molecular gas emission.
A number of stellar formation tracer candidates are projected on two
substructures of the HII region: SH148.83-0.67 and SH149.25-0.00. However, the
lack of molecular gas related to these structures casts doubts on the nature of
the sources. Additional infrared sources may be associated with the HI shell
centered at (l,b) = (149\degr 0\arcmin, -1\degr 30\arcmin).
The most striking active area was found in connection to the HII region LBN
148.11-0.45, where stellar formation candidates are projected onto molecular
gas. The analytical model to the "collect and collapse" process shows that
stellar formation activity could have been triggered by the expansion of this
HII region.Comment: Accepted for publication in MNRAS, 10 pages, 5 figures, 5 table
The unusual hydrocarbon emission from the early carbon star HD 100764: The connection between aromatics and aliphatics
We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope
to obtain spectra of HD 100764, an apparently single carbon star with a
circumstellar disk. The spectrum shows emission features from polycyclic
aromatic hydrocarbons (PAHs) that are shifted to longer wavelengths than
normally seen, as characteristic of ``class C'' systems in the classification
scheme of Peeters et al. All seven of the known class C PAH sources are
illuminated by radiation fields that are cooler than those which typically
excite PAH emission features. The observed wavelength shifts are consistent
with hydrocarbon mixtures containing both aromatic and aliphatic bonds. We
propose that the class C PAH spectra are distinctive because the carbonaceous
material has not been subjected to a strong ultraviolet radiation field,
allowing relatively fragile aliphatic materials to survive.Comment: 11 pages (in emulateapj), 5 tables, 7 figures. Accepted for
publication in Ap
Faint High-Latitude Carbon Stars Discovered by the Sloan Digital Sky Survey: An Initial Catalog
A search of more than 3,000 square degrees of high latitude sky by the Sloan
Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs),
the large majority previously uncataloged. We present homogeneous spectroscopy,
photometry, and astrometry for the sample. The objects lie in the 15.6 < r <
20.8 range, and exhibit a wide variety of apparent photospheric temperatures,
ranging from spectral types near M to as early as F. Proper motion measurements
for 222 of the objects show that at least 50%, and quite probably more than
60%, of these objects are actually low luminosity dwarf carbon (dC) stars, in
agreement with a variety of recent, more limited investigations which show that
such objects are the numerically dominant type of star with C_2 in the
spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of
all known carbon dwarfs, and will grow by another factor of 2-3 by the
completion of the Survey. As the spectra of the dC and the faint halo giant C
stars are very similar (at least at spectral resolution of 1,000) despite a
difference of 10 mag in luminosity, it is imperative that simple luminosity
discriminants other than proper motion be developed. We use our enlarged sample
of FHLCs to examine a variety of possible luminosity criteria, including many
previously suggested, and find that, with certain important caveats, JHK
photometry may segregate dwarfs and giants.Comment: Accepted for publication in The Astronomical Journal, Vol. 127, May
2004, 37 pages, 12 figure
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