arXiv subjects

Biwei Jiang

Publications and source records attributed to Biwei Jiang.

80 records · Page 5Linked to original sources

arXiv2016

On the Silicate Crystallinities of Oxygen-Rich Evolved Stars and Their Mass Loss Rates

For decades ever since the early detection in the 1990s of the emission spectral features of crystalline silicates in oxygen-rich evolved stars, there is a long-standing debate on whether the crystallinity of the silicate dust correlates with the stellar mass loss rate. To investigate the relation between the silicate crystallinities and the mass loss rates of evolved stars, we carry out a detailed analysis of 28 nearby oxygen-rich stars. We derive the mass loss rates of these sources by modeling their spectral energy distributions from the optical to the far infrared. Unlike previous studies in which the silicate crystallinity was often measured in terms of the crystalline-to-amorphous silicate mass ratio, we characterize the silicate crystallinities of these sources with the flux ratios of the emission features of crystalline silicates to that of amorphous silicates. This does not require the knowledge of the silicate dust temperatures which are the major source of uncertainties in estimating the crystalline-to-amorphous silicate mass ratio. With a Pearson correlation coefficient of ~0.24, we find that the silicate crystallinities and the mass loss rates of these sources are not correlated. This supports the earlier findings that the dust shells of low mass-loss rate stars can contain a significant fraction of crystalline silicates without showing the characteristic features in their emission spectra.

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arXiv2016

A Precise Determination of the Mid-Infrared Interstellar Extinction Law Based on the APOGEE Spectroscopic Survey

A precise measure of the mid-infrared interstellar extinction law is crucial to the investigation of the properties of interstellar dust, especially of the grains in the large size end. Based on the stellar parameters derived from the SDSS-III/APOGEE spectroscopic survey, we select a large sample of G- and K-type giants as the tracers of the Galactic mid-infrared extinction. We calculate the intrinsic stellar color excesses from the stellar effective temperatures and use them to determine the mid-infrared extinction for a given line of sight. For the entire sky of the Milky Way surveyed by APOGEE, we derive the extinction (relative to the K$_{\rm S}$ band at wavelength $λ=2.16μ$m) for the four WISE bands at 3.4, 4.6, 12 and 22$μ$m, the four Spitzer/IRAC bands at 3.6, 4.5, 5.8 and 8$μ$m, the Spitzer/MIPS24 band at 23.7$μ$m and for the first time, the AKARI/S9W band at 8.23$μ$m. Our results agree with previous works in that the extinction curve is flat in the ~3--8$μ$m wavelength range and is generally consistent with the $R_V=5.5$ model curve except our determination exceeds the model prediction in the WISE/W4 band. Although some previous works found that the mid-IR extinction law appears to vary with the extinction depth $A_{\rm{K_S}}$, no noticeable variation has been found in this work. The uncertainties are analyzed in terms of the bootstrap resampling method and Monte-Carlo simulation and are found to be rather small.

astro-ph.GA↗

arXiv2016

Revision of Stellar Intrinsic Colors in the Infrared by the Spectroscopic Surveys

Intrinsic colors of normal stars are derived in the popularly used infrared bands involving the 2MASS/JHKs, WISE, Spitzer/IRAC and AKARI/S9W filters. Based on three spectroscopic surveys -- LAMOST, RAVE and APOGEE, stars are classified into groups of giants and dwarfs, as well as metal-normal and metal-poor stars. An empirical analytical relation of the intrinsic color is obtained with stellar effective temperature (Teff) for each group of stars after the zero-reddening stars are selected from the blue edge in the $J-λ$ versus (Teff) diagram. It is found that metallicity has little effect on the infrared colors. In the near-infrared bands, our results agree with previous work. In addition, the color indexes H-W2 and Ks-W1 that are taken as constant to calculate interstellar extinction are discussed. The intrinsic color of M-type stars are derived separately due to lack of accurate measurement of their effective temperature.

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arXiv2016

A systematic search for the spectra with features of crystalline silicates in the Spitzer IRS Enhanced Products

The crystalline silicates features are mainly reflected in infrared bands. The Spitzer Infrared Spectrograph (IRS) collected numerous spectra of various objects and provided a big database to investigate crystalline silicates in a wide range of astronomical environments. We apply the manifold ranking algorithm to perform a systematic search for the spectra with crystalline silicates features in the Spitzer IRS Enhanced Products available. In total, 868 spectra of 790 sources are found to show the features of crystalline silicate. These objects are cross-matched with the SIMBAD database as well as with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)/DR2. The average spectrum of young stellar objects show a variety of features dominated either by forsterite or enstatite or neither, while the average spectrum of evolved objects consistently present dominant features of forsterite in AGB, OH/IR, post-AGB and planetary nebulae. They are identified optically as early-type stars, evolved stars, galaxies and so on. In addition, the strength of spectral features in typical silicate complexes is calculated. The results are available through CDS for the astronomical community to further study crystalline silicate.

astro-ph.GA↗

arXiv2013

Unidentified species in envelopes around carbon stars

The infrared (IR) spectra of many evolved carbon-rich stars exhibit two prominent dust emission features peaking around 21um and 30um, with the former exclusively seen in proto-planetary nebulae (PPNe), while the latter seen in a much wider range of objects, including AGB stars, PPNe and planetary nebulae (PNe). The 30um feature is seen in all the 21um sources, but no correlation is found between these two features. Over a dozen carrier candidates have been proposed for the 21um feature, but none of them has been widely accepted and the nature of the 21um feature remains a mystery. The carrier of the 30um feature also remains unidentied. MgS dust, once widely accepted as a valid carrier, was ruled out because of the sulfur budget problem. In this work we examine nano-sized FeO dust as a carrier for the 21um feature. We calculate the IR emission spectrum of FeO nanodust which undergoes single-photon heating in PPNe. It is found that the 21um feature emitted by FeO nanodust is too broad to explain the observed feature. For the 30um feature, we argue that graphite could be a viable carrier. Graphite, provided its d.c. conductivity sigma_dc exceeding 100/ohm/cm, exhibits a pronounced band at 30um.

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arXiv2011

Modeling Kepler Observations of Solar-like Oscillations in the Red-giant Star HD 186355

We have analysed oscillations of the red giant star HD 186355 observed by the NASA Kepler satellite. The data consist of the first five quarters of science operations of Kepler, which cover about 13 months. The high-precision time-series data allow us to accurately extract the oscillation frequencies from the power spectrum. We find the frequency of the maximum oscillation power, ν_max, and the mean large frequency separation, Δν, are around 106 and 9.4 μHz respectively. A regular pattern of radial and non-radial oscillation modes is identified by stacking the power spectra in an echelle diagram. We use the scaling relations of Δν and ν_max to estimate the preliminary asteroseismic mass, which is confirmed with the modelling result (M = 1.45 \pm 0.05 M_sun) using the Yale Rotating stellar Evolution Code (YREC7). In addition, we constrain the effective temperature, luminosity and radius from comparisons between observational constraints and models. A number of mixed l = 1 modes are also detected and taken into account in our model comparisons. We find a mean observational period spacing for these mixed modes of about 58 s, suggesting that this red giant branch star is in the shell hydrogen-burning phase.

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arXiv2009

Detection of solar-like oscillations from Kepler photometry of the open cluster NGC 6819

Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819 -- one of four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation and the frequency of maximum oscillation power. We find that the asteroseismic parameters allow us to test cluster-membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about two orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler.

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arXiv2009

On Magnesium Sulfide as the Carrier of the 30micron Emission Feature in Evolved Stars

A large number of carbon-rich evolved objects (asymptotic giant branch stars, protoplanetary nebulae, and planetary nebulae) in both the Milky Way galaxy and the Magellanic Clouds exhibit an enigmatic broad emission feature at 30 micron. This feature, extending from 24 micron to 45 micron, is very strong and accounts for up to 30% of the total infrared luminosity of the object. In literature it is tentatively attributed to magnesium sulfide (MgS) dust. Using the prototypical protoplanetary nebula around HD 56126 for illustrative purpose, however, in this work we show that in order for MgS to be responsible for the 30 micron feature, one would require an amount of MgS mass substantially exceeding what would be available in this source. We therefore argue that MgS is unlikely the carrier of the 30 micron feature seen in this source and in other sources as well.

astro-ph.GA↗