Star Extinction Research Articles

A Study of Religious and Scientific Perspectives on Buddhist Cosmology

This research was qualitative, it was to investigate Buddhist cosmology as found in Buddhist scriptures and compare cosmological perspectives between 5 Buddhist scholars and 5 scientists. In Thai Buddhist cosmology, the principles of Paṭiccasamuppāda and Tilakkhaṇa share some similar ideas with the causality principle of science. Scientists regard them as a fundamental universal principle that underpins the laws of nature, which is unsurprising. Another similarity is Saṃsāra, the cycle of rebirth, which may be compared to the birth and extinction of stars but is not comparable to the physical Universe as a whole. Thai Buddhist scholars have accepted that Buddhist and scientific cosmologies are compatible. I argue that when it comes to the physical matter of the universe, its definition, evolution, shape, space, and time, the perspectives of Buddhist scholars and scientists are radically different and cannot be compared. Furthermore, Buddhist and scientific approaches to understanding natural laws are diametrically opposed; Buddhism concentrates on the mind, whilst science concentrates on the physical universe; thus, they cannot be naturally compared.

From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys

We combine high-resolution spectroscopic data from APOGEE-2 survey Data Release 16 (DR16) with broad-band photometric data from several sources as well as parallaxes from Gaia Data Release 2 (DR2). Using the Bayesian isochrone-fitting code StarHorse, we derived the distances, extinctions, and astrophysical parameters for around 388 815 APOGEE stars. We achieve typical distance uncertainties of ∼6% for APOGEE giants, ∼2% for APOGEE dwarfs, and extinction uncertainties of ∼0.07 mag, when all photometric information is available, and ∼0.17 mag if optical photometry is missing. StarHorse uncertainties vary with the input spectroscopic catalogue, available photometry, and parallax uncertainties. To illustrate the impact of our results, we show that thanks to Gaia DR2 and the now larger sky coverage of APOGEE-2 (including APOGEE-South), we obtain an extended map of the Galactic plane. We thereby provide an unprecedented coverage of the disc close to the Galactic mid-plane (|ZGal| < 1 kpc) from the Galactic centre out to RGal ∼ 20 kpc. The improvements in statistics as well as distance and extinction uncertainties unveil the presence of the bar in stellar density and the striking chemical duality in the innermost regions of the disc, which now clearly extend to the inner bulge. We complement this paper with distances and extinctions for stars in other public released spectroscopic surveys: 324 999 in GALAH DR2, 4 928 715 in LAMOST DR5, 408 894 in RAVE DR6, and 6095 in GES DR3.

КОСМІЧНЕ МІКРОХВИЛЬОВЕ ВИПРОМІНЮВАННЯ І ТЕМНА МАТЕРІЯ

The question of the possible origin of one of the components of dark matter filling the galaxies is considered. The analysis of the “fate” of stellar electromagnetic radiation under the conditions of the eternal Universe is taken as a starting point. Based on a comparison of the average lifetime of a star in the active phase and the lifetime of the non-absorbed part of its radiation, it is concluded that the Universe is filled with stellar electromagnetic radiation. However, based on existing concepts, as well as the red shift found in the spectra of distant galaxies, the addition of new radiation to the existing in the Universe will be accompanied by the “disappearance” of radiation in the most long-wave region, that is, there will be a violation of the law of conservation of energy. The main question arises: can radiation as well as energy disappear without a trace? The answer is negative, and it is explained by the involvement of the mechanism of dissipative losses during the radiative transfer by the expanses of the Universe. For this purpose, an assumption is introduced about the presence of an agent's medium interacting with quanta of radiation with the help of excessively weak forces. It is hypothesized that photons that fall into the low-frequency region (microwave band and ranges close to it) are able to pair up in an agent's medium, creating neutral particles of extremely small masses (about 0.0013 eV). These particles - bosons - are particles of the agent itself. Based on the nature of the agent, some observational data related to the Solar System (increased distance between the Sun and the Earth, the "floating" value of the G gravitation constant, scintillations of cosmic microwave radiation), as well as detected deviations observed during spacecraft acceleration with gravitational slingshots near the Earth (Galileo, NEAR, Rosetta, Messenger, Cassini). In addition, this hypothesis regarding the origin and properties of the agent explains some of the results of laboratory research: scintillations of the rates of chemical and biochemical reactions, floating "zero" of high-precision instruments and, possibly, relaxation processes in elastic solids (material aging). The main conclusions: cosmic microwave radiation is a remnant of stellar radiation, and the agent's medium is a component of dark matter, which is closely associated with cosmic microwave radiation. Other dark matter components are extinct stars, their various cold fragments, including gases and dust, and possibly other deeper structural levels of matter.

Discussion on Fundamental Problems of Physics Hidden in Cosmology

Discussion on Fundamental Problems of Physics Hidden in Cosmology

THE GRAY EXTINCTION OF THE IONIZING CLUSTER IN NGC 3603 FROM ULTRAVIOLET TO OPTICAL WAVELENGTHS

ABSTRACT We use photometry in the F220W, F250W, F330W, F435W filters from the High Resolution Channel of the Advanced Camera for Surveys and photometry in the F555W, F675W, and F814W filters from the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope to derive individual stellar reddenings and extinctions for stars in the HD 97950 cluster in the giant H ii region NGC 3603. The mean line of sight reddening for about a hundred main-sequence member stars inside the cluster is E ( F 435 W − F 555 W ) = 1.33 ± 0.12 ?> mag. After correcting for foreground reddening, the total to selective extinction ratio is R F 555 W = 3.75 ± 0.87 ?> in the cluster. Within the standard deviation associated with E ( λ − F 555 W ) / E ( F 435 W − F 555 W ) ?> in each filter, the cluster extinction curve at ultraviolet wavelengths tends to be grayer than the average Galactic extinction laws from Cardelli et al. and Fitzpatrick. It is closer to the extinction law derived by Calzetti et al. for starburst galaxies, where the 0.2175 μm bump is absent. This indicates an anomalous extinction in the HD 97950 cluster, which may due to the clumpy dust distribution within the cluster, and the size of dust grains being larger than the average Galactic ISM.

Measure the distance and extinction for stars in LAMOST survey with Bayesian method

Measure the distance and extinction for stars in LAMOST survey with Bayesian method

3D Galactic extinction modelling

AbstractUsing multi-band photometry we train a forward model to emulate the colour-change due to temperature and extinction for stars. We simultaneously solve for the astrophysical parameters (APs) extinction A0, temperature Teff and distance modulus μr in a Bayesian framework for individual stars. We introduce an HRD prior to account for previous knowledge about the distribution of stars in the temperature- absolute magnitude plane (see also Bailer-Jones 2011). This allows us to infer distance information. We obtain the full three dimensional PDFs of all the stars in a field, allowing us to determine extinction-distance profiles for a given line of sight.

Star formation in Cometary Globule 1: the second generation

C18O spectral line observations, NIR spectrosopy, narrow and broad band NIR imaging and stellar J,H,Ks photometry are used to analyse the structure of the archetype cometary globule 1 (CG 1) head and the extinction of stars in its direction. A young stellar object (YSO) associated with a bright NIR nebulosity and a molecular hydrogen object (a probable obscured HH-object), were discovered in the globule. Molecular hydrogen and Br_gamma line emission is seen in the direction of the YSO. The observed maximum optical extinction in the globule head is 9.2 magnitudes. The peak N(H2) column density and the total mass derived from the extinction are 9.0 10^21 cm-2 and and 16.7 Msun (d/300pc)^2. C18O emission in the globule head is detected in a 1.5'' by 4' area with a sharp maximum SW of the YSO. Three regions can be discerned in C18O line velocity and excitation temperature. Because of variations in the C18O excitation temperature the integrated line emission does not follow the optical extinction. It is argued that the variations in the C18O excitation temperatures are caused by radiative heating by NX Pup and interaction of the YSO with the parent cloud. No indication of a strong molecular outflow from the YSO is evident in the molecular line data. The IRAS point source 07178-4429 located in the CG 1 head resolves into two sources in the HIRES enhanced IRAS images. The 12 and 25 micron emission originates mainly in the star NX Puppis and the 60 and 100 micron emission in the YSO. The IRAS FIR luminosity of the YSO is 3.1 Lsun.

MAGNETIC FIELD CONFIGURATION AT THE GALACTIC CENTER INVESTIGATED BY WIDE-FIELD NEAR-INFRARED POLARIMETRY: TRANSITION FROM A TOROIDAL TO A POLOIDAL MAGNETIC FIELD

We present a large-scale view of the magnetic field (MF) in the central 2° × 2° region of our Galaxy. The polarization of point sources has been measured in the J, H, and KS bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m Infrared Survey Facility telescope. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we obtain polarization originating from magnetically aligned dust grains in the central few hundred parsecs of our Galaxy. We find that near the Galactic plane, the MF is almost parallel to the Galactic plane (i.e., toroidal configuration), but at high Galactic latitudes (∣b ∣ >04) the field is nearly perpendicular to the plane (i.e., poloidal configuration). This is the first detection of a smooth transition of the large-scale MF configuration in this region.

The ilium forward modelling algorithm for multivariate parameter estimation and its application to derive stellar parameters fromGaiaspectrophotometry

I introduce an algorithm for estimating parameters from multidimensional data based on forward modelling. In contrast to many machine learning approaches it avoids fitting an inverse model and the problems associated with this. The algorithm makes explicit use of the sensitivities of the data to the parameters, with the goal of better treating parameters which only have a weak impact on the data. The forward modelling approach provides uncertainty (full covariance) estimates in the predicted parameters as well as a goodness-of-fit for observations. I demonstrate the algorithm, ILIUM, with the estimation of stellar astrophysical parameters (APs) from simulations of the low resolution spectrophotometry to be obtained by Gaia. The AP accuracy is competitive with that obtained by a support vector machine. For example, for zero extinction stars covering a wide range of metallicity, surface gravity and temperature, ILIUM can estimate Teff to an accuracy of 0.3% at G=15 and to 4% for (lower signal-to-noise ratio) spectra at G=20. [Fe/H] and logg can be estimated to accuracies of 0.1-0.4dex for stars with G<=18.5. If extinction varies a priori over a wide range (Av=0-10mag), then Teff and Av can be estimated quite accurately (3-4% and 0.1-0.2mag respectively at G=15), but there is a strong and ubiquitous degeneracy in these parameters which limits our ability to estimate either accurately at faint magnitudes. Using the forward model we can map these degeneracies (in advance), and thus provide a complete probability distribution over solutions. (Abridged)

Ne ISOTOPES IN INDIVIDUAL PRESOLAR GRAPHITE GRAINS FROM THE MURCHISON METEORITE TOGETHER WITH He, C, O, Mg-Al ISOTOPIC ANALYSES AS TRACERS OF THEIR ORIGINS

Ne isotopes measured in individual presolar graphite grains, solid samples of extinct stars preserved in primitive meteorites, provide information on the type of stellar sources of the grains and on nucleosynthetic mixing and ion-trapping processes which were operating. We present Ne and He isotope analyses of single presolar graphite grains from the KFB1 density fraction extracted from the carbonaceous chondrite Murchison. In addition, we measured isotopes of C, O, and Mg-Al with the NanoSIMS ion microprobe to better constrain the origin of the grains. Eleven out of 51 presolar graphite grains contain nucleosynthetic {sup 22}Ne above our detection limit. This fraction of {sup 22}Ne-rich grains is similar to the one reported by Nichols et al. although we have a lower {sup 22}Ne detection limit. We detected rare He-shell {sup 20}Ne in one {sup 22}Ne-rich grain and obtained the {sup 20}Ne/{sup 22}Ne ratio (0.03 {+-} 0.02) of the He-shell of an Asymptotic Giant Branch (AGB) star with 1.5-2 M {sub sun} and subsolar metallicity. We also detected {sup 4}He in this grain, while in the other grains, which originally acquired He, He-loss seems to be significant. We found unequivocal evidence for radiogenic {sup 22}Ne (Ne-R) in another graphite grain, which likelymore » condensed in a core-collapse supernova and which incorporated live radioactive {sup 22}Na (t {sub 1/2} = 2.6 yr). For the other grains, a clear assignment to a stellar source is more difficult to make. Putative stellar sources are supernovae, AGB stars, born-again AGB stars, J-type carbon stars, and CO novae.« less

MAGNETIC FIELD CONFIGURATION AT THE GALACTIC CENTER INVESTIGATED BY WIDE FIELD NEAR-INFRARED POLARIMETRY

We present a polarimetric map of a 20' × 20' area toward the Galactic center. The polarization of point sources has been measured in the J, H, and KS bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m telescope IRSF. One percent or better accuracy of polarization degree is achieved for sources with J < 14.5, H < 13.5, and KS < 12.0. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we have obtained a polarization originating from magnetically aligned dust grains at the central region of our Galaxy of at most 1–2 kpc. The distribution of the position angles shows a peak at ∼20°, nearly parallel to the Galactic plane, suggesting a toroidal magnetic configuration. The derived direction of the magnetic field is in good agreement with that obtained from far-infrared/submillimeter observations, which detect polarized thermal emission from dust in the molecular clouds at the Galactic center. Our results show that, by subtracting foreground components, near-infrared polarimetry allows investigation of the magnetic field structure at the Galactic center.

The influence of scattering on the extinction of stars

Aims. In photometric measurements of stars, one usually assumes that all photons have reached the observer on a direct path and neglects the fraction that has been scattered. However, in observations of distant stars, for instance when they are in another galaxy, this fraction is not negligible. We investigate how scattered light enhances the flux and affects the extinction curve. Methods. We compute the radiative transfer in a dusty medium using various techniques at wavelengths where dust emission is absent. Among the configurations considered are: a) homogeneous spheres with a central star; b) an infinite layer of stars behind or mixed with an infinite layer of dust which may be homogeneous or clumpy; c) one star in or behind a homogeneous or clumpy block of dust. In all cases, we define in analogy to the extinction optical depth τ an effective optical thickness τ eff such that the flux attenuation is given by the factor exp(−τ eff ). Results. a) We compute τ eff and analyze how it depends, in different geometries, on the extinction optical depth, the dust albedo, the scattering phase function and the spatial resolution of the measurement; b) we calculate effective extinction curves towards single stars in clumpy and homogeneous media adopting standard optical dust properties. They show marked differences to the standard reddening curve; c) when determining τ eff for a collection of spatially unresolved stars, we find discrepancies with some of the results in the literature. Conclusions. When one converts the apparent magnitude of a star or a star cluster into an absolute magnitude, scattered light should be taken into account whenever the spatial resolution with which the measurement was performed corresponds to a linear scale over which the scattering optical depth around the source is greater than the relative observational error. One may try to determine τ eff by solving the radiative transfer for an assumed distribution of stars and dust, or search for representative calculations in the literature, for example in the figures of this paper.

Globular Cluster Archaeology: Hydrogen‐burning Nucleosynthesis and Extra Mixing in Extinct Stars

We compute the evolution of the surface CNO abundances in two types of stars that might have contributed to the star-to-star abundance variations in globular clusters: intermediate-mass asymptotic giant branch stars and low-mass upper red giant branch stars. We show that abundances of [C/Fe] -1 accompanied by apparent signatures of oxygen processing, such as very high [N/Fe] or negative [O/Fe], as observed in some of the globular cluster subgiants and red giants, cannot originate from hot-bottom burning in intermediate-mass asymptotic giant branch stars. This is a robust nucleosynthesis prediction. At the same time, such peculiar CNO abundances could come from the vicinity of the hydrogen-burning shell in upper red giant branch stars, provided that some of them had experienced enhanced extra mixing in the past themselves.

Young Stars at the Center of the Milky Way?

We present results from the first diffraction-limited images of the Galactic center (GC) at 1.6, 2.1, and 3.8 μm with the new adaptive optics (AO) camera NAOS/CONICA at the ESO Very Large Telescope, as well as 3-4 μm low-resolution spectroscopy. We have discovered a small (0.13 lt-yr diameter) cluster of compact sources about 05 north of IRS 13 with strong IR excesses due to T > 500 K dust. The nature of the sources is unclear. They may be a cluster of highly extincted stars that heat the local environment of the minispiral. We also consider an explanation that involves the presence of young stars at evolutionary stages between young stellar objects and Herbig Ae/Be objects with ages of about 0.1 to 1 million yr. This scenario would imply more recent star formation in the GC than previously suspected. The AO observations also resolve the central IRS 13 complex. In addition to the previously known bright stars E1 and E2, the K- and L'-band images for the first time resolve object E3 into two components, E3N and E3c. The latter one is closest to the 7 mm Very Large Array radio continuum source found at the location of the IRS 13 complex. E3c may be associated with a strong stellar wind or a dusty Wolf-Rayet-like star at that location.

Observing the Formation of the Hubble Sequence in the Great Observatories Origins Deep Survey

Understanding the physical formation of the Hubble sequence remains one of the most important unsolved astrophysical problems. Searches for proto-disks and proto-ellipticals can now be effectively done using deep wide-field Hubble Space Telescope images taken with the new Advanced Camera for Surveys. Through an analysis of concentrations (C), asymmetries (A) and clumpiness values (S) (CAS) of galaxies found in the GOODS Field South, we are able to identify objects possibly forming onto the Hubble sequence. Using this approach, we detect a sizeable population of star forming luminous diffuse objects and star forming luminous asymmetric objects between redshifts 0.5 2 and z < 1. The luminous asymmetric objects are found at a similar abundance, with a peak at z~1. We argue that these galaxies are a subset of modern disks and ellipticals in formation. The co-moving volume density of the luminous diffuse objects between z = 1 - 2 is similar to the local density of bright disk galaxies, with values ~5*10^{5} Gpc^{-3}. The SEDs of these objects are mostly consistent with starbursts, or star-forming normal galaxies, with average uncorrected for extinction star formation rates of ~4 M_0 yr^{-1}. These galaxies also host 35-40% of the star formation activity at 1 < z < 2. We briefly discuss the implications of these objects for understanding the origin of the Hubble sequence.

Coronagraphic imaging on the VLTI with VIDA

In a few years, the VLTI will be able to combine light from 4 to 8 telescopes equipped with adaptive optics. In order to exploit the full VLTI infrastructure, a second generation instrument, based on the densified pupil concept (VIDA), has been proposed for very high resolution direct imaging and coronagraphy. This paper presents some possible coronagraphic devices providing a total star extinction on the VLTI when there are no phase errors. Lastly, the expected performances considering cophasing and adaptive optics residual errors are also presented.

New MIR Excess Sources north of the IRS 13 Complex

The ISAAC and NAOS/CONICA systems on the ESO VLT UT1 and UT4 telescopes have been used to image the central stellar cluster of the Milky Way in the MIR L and M band (3.3 μm and 4.6 μm) in order to obtain new information on the stellar populations within the central cluster. The NAOS/CONICA adaptive optics images of unprecedented sharpness and sensitivity have resulted in the detection of a small cluster (<0.13 light years) of 7 compact sources with a strong infrared excess. Our MIR imaging and spectroscopy data clearly show that this excess is due to the contribution of warm T < 500 K dust. The nature of these newly found sources is currently unclear. Three possible explanations are mentioned and briefly discussed: 1) The L band excess sources north of the IRS 13 complex may be heavily extincted luminous stars; 2) They may be hot stars that heat the more ambient environment of the local mini-spiral; 3) Finally the newly found objects may even be young stars with luminous accretion disks.

Spectral Irradiance Calibration in the Infrared. XIII. "Supertemplates" and On-Orbit Calibrators for theSIRTFInfrared Array Camera

We describe the technique that will be used to develop a set of on-orbit calibrators for the Infrared Array Camera (IRAC) and demonstrate the validity of the method for stars with spectral types either K0–M0 III or A0–A5 V. For application to SIRTF, the approach is intended to operate with all available optical, near-infrared (NIR), and mid-infrared (MIR) photometry and to yield complete absolute spectra from UV to MIR. One set of stars is picked from Landolt's extensive network of optical (UBVRI) calibrators, the other from the Carter-Meadows set of faint IR standards. Traceability to the Cohen-Walker-Witteborn framework of absolute photometry and stellar spectra is assured. The method is based on the use of either supertemplates, which represent the intrinsic shapes of the spectra of K0–M0 III stars from far-UV (1150 A) to MIR (35 μm) wavelengths, or Kurucz synthetic spectra for A0–A5 V stars. Each supertemplate or Kurucz model is reddened according to the individual star's extinction and is normalized using available characterized optical photometry. This paper tests our capability to predict NIR (JHK) magnitudes using supertemplates or models constrained by Hipparcos/Tycho or precision ground-based optical data. We provide absolutely calibrated 0.275–35.00 μm spectra of 33 Landolt and Carter-Meadows optical standard stars to demonstrate the viability of this technique, and to offer a set of IR calibrators 100–1000 times fainter than those we have previously published. As an indication of what we can expect for actual IRAC calibration stars, we have calculated the absolute uncertainties associated with predicting the IRAC magnitudes for the faintest cool giant and hot dwarf in this new set of calibration stars.

Extinction Mapping of the Bipolar Outflow NGC 2346

We have acquired narrowband imaging of NGC 2346 in the transitions H I λ6563 and λ4861 and [O III] λ5007. As a result, we are able to evaluate the variation of both excitation and extinction over the projected central parts of the nebular shell. Extinction appears to be surprisingly uniform, and there is (in particular) little evidence for the reddening asymmetries proposed in previous analyses. Cusplike enhancements in Av at the periphery of the source are attributed to a layer of extincting material at the limits of the H II region, implying a value of major-axis reddening ΔAv < 0.5 mag. Similar extinctions are also deduced from an analysis of infrared and millimeter-wavelength observations. It is unclear what proportion of this reddening may be attributed to the molecular belt, although it seems likely that this feature contributes ~0.3 mag of extinction in the northern lobe and explains the north-south asymmetries noted in optical images. Given that levels of local extinction are quite modest, it seems likely that the larger part of the observed reddening (Av ≈ 2 mag) arises from intervening interstellar material, a conclusion that is again at variance with previous analyses. Such a presumption would explain the relative uniformity in extinction over the face of the nebula, and similarity between distances estimated from extinction and those determined through alternative analyses. If this is accepted, however, then it follows that prior estimates of central star extinction must be greatly in error. One possible origin for this error is noted from Hubble Space Telescope imagery in [N II] λ6584, where it is clear that a secondary star is located close to the presumed A-type central star, a component that was not allowed for in previous analyses. It is unclear whether this star is physically associated with the core binary system.