55 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
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
Cool carbon stars in the halo: new very red or distant objects
The goal of this paper is to present and analyse a new sample of cool carbon
(C)stars located in the halo. Twenty three new C stars were discovered. Spectra
are typical of N-type stars with C2 and CN bands and sometimes Halpha in
emission. ... Four objects are particularly red with J-K > 3, with 2 located at
more than 5 kpc. from the Galactic plane. Eight additional objects with similar
properties are found in the literature and our previous works. These 12 C stars
could be useful to study mass loss at low metallicity. Two objects are at
distances of 95 and 110 kpc. They are located in the region with galactocentric
Z < -60 kpc in which the model of Law et al. predicts the Sgr stream to have a
loop. (Abstact abridged)Comment: 16 pages, 12 figures, accepted by A
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, ÎČ-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 350â2,500 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 ÎČ-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 > ÎČ-carotene > dry
matter> total phenols = titratable acidity â„ soluble solids > taste index > flavonoids
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
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
Reprocessing the Hipparcos data for evolved stars III Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
We analyze the K band luminosities of a sample of galactic long-period
variables using parallaxes measured by the Hipparcos mission. The parallaxes
are in most cases re-computed from the Hipparcos Intermediate Astrometric Data
using improved astrometric fits and chromaticity corrections. The K band
magnitudes are taken from the literature and from measurements by COBE, and are
corrected for interstellar and circumstellar extinction. The sample contains
stars of several spectral types: M, S and C, and of several variability
classes: Mira, semiregular SRa, and SRb. We find that the distribution of stars
in the period-luminosity plane is independent of circumstellar chemistry, but
that the different variability types have different P-L distributions. Both the
Mira variables and the SRb variables have reasonably well-defined
period-luminosity relationships, but with very different slopes. The SRa
variables are distributed between the two classes, suggesting that they are a
mixture of Miras and SRb, rather than a separate class of stars. New
period-luminosity relationships are derived based on our revised Hipparcos
parallaxes. The Miras show a similar period-luminosity relationship to that
found for Large Magellanic Cloud Miras by Feast et al. (1989). The maximum
absolute K magnitude of the sample is about -8.2 for both Miras and
semi-regular stars, only a little fainter than the expected AGB limit. We show
that the stars with the longest periods (P>400d) have high mass loss rates and
are almost all Mira variables.Comment: Comments welcome. Submitted to A&A 11 pages, 7 figs, 3 table
R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2
Rare types of variable star may give unique insight into short-lived stages
of stellar evolution. The systematic monitoring of millions of stars and
advanced light curve analysis techniques of microlensing surveys make them
ideal for discovering also such rare variable stars. One example is the R
Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We
have conducted a systematic search of the EROS-2 database for the Galactic
catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of
100 million stars, monitored for 6.7 years (from July 1996 to February
2003), have been analysed to search for the main signature of RCB stars, large
and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm
the photometric candidates. We have discovered 14 new RCB stars, all in the
direction of the Galactic Bulge, bringing the total number of confirmed
Galactic RCB stars to about 51. After reddening correction, the colours and
absolute magnitudes of at least 9 of the stars are similar to those of
Magellanic RCB stars. This suggests that these stars are in fact located in the
Galactic Bulge, making them the first RCB stars discovered in the Bulge. The
localisation of the 5 remaining RCBs is more uncertain: 4 are either located
behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual
thick circumstellar shell; the other is a DY Per RCB which may be located in
the Bulge, even if it is fainter than the known Magellanic DY Per. From the
small scale height found using the 9 new Bulge RCBs,
pc (95% C.L.), we conclude that the RCB stars follow a disk-like distribution
inside the Bulge.Comment: 20 pages, 26 figures, Accepted in A&
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: Methods and Initial Results
We report the discovery of 39 Faint High Latitude Carbon Stars (FHLCs) from
Sloan Digital Sky Survey commissioning data. The objects, each selected
photometrically and verified spectroscopically, range over 16.6 < r* < 20.0,
and show a diversity of temperatures as judged by both colors and NaD line
strengths. At the completion of the Sloan Survey, there will be many hundred
homogeneously selected and observed FHLCs in this sample. We present proper
motion measures for each object, indicating that the sample is a mixture of
extremely distant (>100 kpc) halo giant stars, useful for constraining halo
dynamics, plus members of the recently-recognized exotic class of very nearby
dwarf carbon (dC) stars. Motions, and thus dC classification, are inferred for
40-50 percent of the sample, depending on the level of statistical significance
invoked. The new list of dC stars presented here, although selected from only a
small fraction of the final SDSS, doubles the number of such objects found by
all previous methods. (Abstract abridged).Comment: Accepted for publication in The Astronomical Journal, Vol. 124, Sep.
2002, 40 pages, 7 figures, AASTeX v5.
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