LAMOST Spectroscopy and Gaia Photo-Astrometry for an Interstellar Extinction Study

view Abstract Citations (75) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The galactic extinction of extragalactic objects. I - The csc B law and the extinction coefficient. de Vaucouleurs, G. ; Buta, R. Abstract Data on galaxies are used to determine the effects of galactic extinction on extragalactic objects. Counts of faint galaxies and of galactic clusters are used to establish the presence of extinction in the polar caps and the statistical validity of the csc b law right up to the poles. The mean surface brightness of bright galaxies and the hydrogen index, measuring the neutral hydrogen to luminosity ratio, are used to evaluate the total B-band extinction coefficient. The color excesses of bright galaxies in B-V and U-B are applied to evaluate the reddening coefficient which provides a third, independent estimate of the polar extinction. It is shown that all these indicators are in much better agreement with the extinction model proposed by de Vaucouleurs, de Vaucouleurs, and Corwin (1976) than with the one proposed by McClure and Crawford (1971). Publication: The Astronomical Journal Pub Date: July 1983 DOI: 10.1086/113380 Bibcode: 1983AJ.....88..939D Keywords: Astrometry; Galactic Clusters; Galaxies; Interstellar Extinction; Milky Way Galaxy; Brightness; Coefficients; Color; Distance; Luminosity; Astrophysics full text sources ADS | data products SIMBAD (1)

With the photometric data from the SDSS survey, the spectroscopic data from the SDSS/SEGUE and the LAMOST surveys, and the astrometric data from the Gaia DR2, we have identified 67 highly probable member stars of the GD-1 cold stellar stream spread along almost its entire length (i.e., from 126° to 203° in R.A.). With the accurate spectroscopic (i.e., metallicity and line-of-sight velocity) and astrometric (i.e., proper motions) information, the position–velocity diagrams, i.e., ϕ 1–μ α , ϕ 1–μ δ , and ϕ 1–v gsr, of the GD-1 stream are well mapped. The stream has an average metallicity [Fe/H] = −1.96. The rich information of member stars of the stream now available allow one not only to model its origin, but also to place strong constraints on the mass distribution and the gravitational potential of the Milky Way.

A detailed knowledge about the galactic extinction is mandatory to obtain the astrophysical/kinematical parameters time variation outside the solar neighbourhood. One may hope that the GAIA photometry itself will contribute to colour excess determinations for most of the sample otherwise the extinction must be deduced from external sources. 3D galactic models where the dust distribution is an integral part seems a viable solution.

view Abstract Citations (73) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The variation of galactic interstellar extinction in the ultraviolet. Witt, A. N. ; Bohlin, R. C. ; Stecher, T. P. Abstract The interstellar extinction in the UV (3.25 μm-1 ≤ λ-1 ≤ 8.0 μm-1) has been determined from IUE spectra for 29 reddened early-type stars by use of the pair method. The star sample was selected on the basis of highly deviant ratios of the strength of the 4430 Å diffuse interstellar absorption feature to color excess E(B-V) (15 stars) and on the basis of association with reflection nebulae (9 stars). The incidence of peculiar extinction curves among this sample as measured by significant deviations from the mean galactic extinction law is near 70%. Correlations of peculiar extinction with cloud environments are investigated. Previous studies that show variation in UV extinction characteristics with galactic longitude or with association with specific galactic spiral arms are confirmed. Publication: The Astrophysical Journal Pub Date: April 1984 DOI: 10.1086/161934 Bibcode: 1984ApJ...279..698W Keywords: Early Stars; Galactic Radiation; Interstellar Extinction; Ultraviolet Astronomy; Astronomical Coordinates; Iue; Milky Way Galaxy; Astrophysics full text sources ADS | data products SIMBAD (48) MAST (1)

V404 Cygni is a well-known candidate for the black hole binary thought to have relativistic jets. It showed extreme outbursts in 2015 June, characterized by a large amplitude and short time variation of flux in the radio, optical, and X-ray bands. Not only disk emission but also synchrotron radiation from the relativistic jets was suggested by radio observations. However, it is difficult to measure the accurate spectral shape in the optical/near-infrared band because there are uncertainties of interstellar extinction. To estimate the extinction value for V404 Cygni, we performed photopolarimetric and spectroscopic observations of V404 Cygni and nearby field stars. Here, we estimate the Galactic extinction using interstellar polarization based on the observation that the origin of the optical polarization is the interstellar medium, and investigate the properties of interstellar polarization around V404 Cygni. We found a good correlation between the color excess and polarization degree in the field stars. We also confirmed that the wavelength dependence of the polarization degree in the highly polarized field stars was similar to that of V404 Cygni. Using the highly polarized field stars, we estimated the color excess for the (B − V) color and the extinction in the V band to be E(B − V) = 1.2 ± 0.2 and 3.0 < A(V) < 3.6, respectively. A tendency for a bluer peak of polarization (λmax < 5500 Å) was commonly seen in the highly polarized field stars, suggesting that the dust grains toward this region are generally smaller than the Galactic average. The corrected spectral energy distribution of V404 Cygni in the near-infrared and optical bands in our results indicated a spectral break between 2.5 × 1014 Hz and 3.7 × 1014 Hz, which might originate in the synchrotron self-absorption.

We have developed our original made-to-measure (M2M) algorithm, PRIMAL, with the aim of modelling the Galactic disc from upcoming Gaia data. From a Milky Way like N-body disc galaxy simulation, we have created mock Gaia data using M0III stars as tracers, taking into account extinction and the expected Gaia errors. In PRIMAL, observables calculated from the N-body model are compared with the target stars, at the position of the target stars. Using PRIMAL, the masses of the N-body model particles are changed to reproduce the target mock data, and the gravitational potential is automatically adjusted by the changing mass of the model particles. We have also adopted a new resampling scheme for the model particles to keep the mass resolution of the N-body model relatively constant. We have applied PRIMAL to this mock Gaia data and we show that PRIMAL can recover the structure and kinematics of a Milky Way like barred spiral disc, along with the apparent bar structure and pattern speed of the bar despite the galactic extinction and the observational errors.

Context. Globular clusters (GCs) in the Milky Way (MW) bulge are very difficult to study for the following reasons: (i) they suffer from the severe crowding and Galactic extinction, which are characteristic of these inner Galactic regions; (ii) they are more prone to the effects of dynamical processes. Therefore, they are relatively faint and difficult to map. However, deep, near-infrared photometry like that provided by the VISTA variables in the Via Láctea Extended Survey (VVVX) allows us to map GCs in this crucial yet relatively uncharted region. Aims. Our main goals are to study the true nature of the GC candidates FSR 19 and FSR 25 and measure their physical parameters. Methods. We used the near-infrared VVVX database, in combination with the Two Micron All Sky Survey and Gaia EDR3 proper motions (PMs) and photometry to study ages, metallicities, distances, reddening, mean PMs, sizes, and integrated luminosities for FSR 19 and FSR 25. A robust combination of selection criteria allowed us to effectively clean interlopers among our samples. Results. Our results confirm with a high level of confidence that both FSR 19 and FSR 25 are genuine MW bulge GCs. Each of the performed tests and resulting parameters provide clear evidence of the GC nature of these targets. We derive distances of 7.2 ± 0.7 kpc and D = 7.0 ± 0.6 (corresponding to distance moduli of 14.29 ± 0.08 and 14.23 ± 0.07) for FSR 19 and FSR 25, respectively. Their ages and metallicities are 11 Gyr and [Fe/H] = −0.5 dex for both clusters, which were determined from Dartmouth and PARSEC isochrone fitting. The integrated luminosities are MKs(FSR 19) = −7.72 mag and MKs(FSR 25) = −7.31 mag, which places them in the faint tail of the GC luminosity function. By adopting a King profile for their number distribution, we determine their core and tidal radii (rc, rt). For FSR 19, rc = 2.76 ± 0.36 pc and rt = 5.31 ± 0.49 pc, while FSR 25 appears more extended with rc = 1.92 ± 0.59 pc and rt = 6.85 ± 1.78 pc. Finally, their mean GC PMs (from Gaia EDR3) are μα* = −2.50 ± 0.76 mas yr−1, μδ = −5.02 ± 0.47 mas yr−1 for FSR 19 and μα* = −2.61 ± 1.27 mas yr−1, μδ = −5.23 ± 0.74 mas yr−1 for FSR 25. Conclusion. We demonstrate and confirm, based on the measured astrophysical parameters, that the two target clusters are indeed genuine and of low luminosity relatively metal-rich old GCs in the bulge of the MW.

The high-resolution palaeoclimatic and palaeoceanographic history of the last 24,000 years in the central Aegean Sea, Greece

We develop, validate and apply a forward model to estimate stellar atmospheric parameters (Teff, log g, and [Fe/H]), revised distances and extinctions for 220 million stars with XP spectra from Gaia DR3. Instead of using ab initio stellar models, we develop a data-driven model of Gaia XP spectra as a function of the stellar parameters, with a few straightforward built-in physical assumptions. We train our model on stellar atmospheric parameters from the LAMOST survey, which provides broad coverage of different spectral types. We model the Gaia XP spectra with all of their covariances, augmented by 2MASS and WISE photometry that greatly reduces degeneracies between stellar parameters, yielding more precise determinations of temperature and dust reddening. Taken together, our approach overcomes a number of important limitations that the astrophysical parameters released in Gaia DR3 faced, and exploits the full information content of the data. We provide the resulting catalogue of stellar atmospheric parameters, revised parallaxes, and extinction estimates, with all their uncertainties. The modelling procedure also produces an estimate of the optical extinction curve at the spectral resolution of the XP spectra (R ∼ 20–100), which agrees reasonably well with the R(V) = 3.1 CCM model. Remaining limitations that will be addressed in future work are that the model assumes a universal extinction law, ignores binary stars and does not cover all parts of the Hertzsprung–Russell Diagram (e.g. white dwarfs).

Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily-reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both 2D and 3D extinction maps, using independent extinction measures based on a large spectroscopic sample of stars towards the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution $H$-band APOGEE spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants towards the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, 2D bulge extinction maps and 3D extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the 2D and 3D extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.

In this study, 21 simple sequence repeat (SSR) markers were used to evaluate the genetic diversity and population structure among 77 Perilla accessions from high-latitude and middle-latitude areas of China. Ninety-five alleles were identified with an average of 4.52 alleles per locus. The average polymorphic information content (PIC) and genetic diversity values were 0.346 and 0.372, respectively. The level of genetic diversity and PIC value for cultivated accessions of Perilla frutescens var. frutescens from middle-latitude areas were higher than accessions from high-latitude areas. Based on the dendrogram of unweighted pair group method with arithmetic mean (UPGMA), all accessions were classified into four major groups with a genetic similarity of 46%. All accessions of the cultivated var. frutescens were discriminated from the cultivated P. frutescens var. crispa. Furthermore, most accessions of the cultivated var. frutescens collected in high-latitude and middle-latitude areas were distinguished depending on their geographical location. However, the geographical locations of several accessions of the cultivated var. frutescens have no relation with their positions in the UPGMA dendrogram and population structure. This result implies that the diffusion of accessions of the cultivated Perilla crop in the northern areas of China might be through multiple routes. On the population structure analysis, 77 Perilla accessions were divided into Group I, Group II, and an admixed group based on a membership probability threshold of 0.8. Finally, the findings in this study can provide useful theoretical knowledge for further study on the population structure and genetic diversity of Perilla and benefit for Perilla crop breeding and germplasm conservation.

We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond, (2) average over dust compositions, and (3) mischaracterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly overestimated. In particular, the stellar luminosity is most likely in the range 104.8 < L */L ☉ < 105.0 and the star was not extremely massive for a Type IIP progenitor, with M * < 15 M ☉. Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw, the star was probably obscured by an ongoing wind with to 10−5.0 M ☉ yr−1 at the time of the explosion, roughly consistent with the expected mass-loss rates for a star of its temperature (T * ≃ 3600+300 − 200 K) and luminosity. In the spirit of Galactic extinction laws, we supply simple interpolation formulae for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength (λ ⩾ 0.3 μm) and total (absorption plus scattering) V-band optical depth (τ V ⩽ 20). These do not include the contributions of dust emission, but provide a simple, physical alternative to incorrectly using interstellar extinction laws.

The nature of Galactic interstellar extinction is tested using reddening line parameters for several fields in conjunction with equivalent widths W(λ4430) for the diffuse interstellar band at 4430 Å. The Cardelli et al. relations (Astrophys. J. 345, 245 (1989). doi:10.1086/167900) at infrared, optical, and ultraviolet wavelengths are inconsistent with the newly-derived quadratic variation of RV(observed) on reddening slope X. A minimum of RV = 2.82 ± 0.06 exists for X = 0.83 ± 0.01, and is argued to represent true Galactic extinction described by A(λ) ∝ λ–1.375. It matches expectations for a new description of extinction in the infrared, optical, and ultraviolet by Zagury (Astron. Nachr. 334, 1107 (2013)). Additional consequences, reddened stars with no 2175 Å feature and a correlation of normalized λ4430 absorption with X, are not predicted by the Cardelli et al. relation (Astrophys. J. 345, 245 (1989). doi:10.1086/167900 ). Known variations in X from 0.62 to 0.83, and corresponding variations in RV(observed) from 4.0 to 2.8, presumably result from forward-scattered starlight in the ultraviolet contaminating optical light of stars affected by dust extinction. A new understanding of the true nature of interstellar extinction is important for establishing an accurate picture of the extragalactic distance scale, which in turn is related to our understanding of the nature of the Universe.

ABSTRACTThis paper addresses the issue of how best to correct astronomical data for the wavelength‐dependent effects of Galactic interstellar extinction. The main general features of extinction from the IR through the UV are reviewed, along with the nature of observed spatial variations. The enormous range of extinction properties found in the Galaxy, particularly in the UV spectral region, is illustrated. Fortunately, there are some tight constraints on the wavelength dependence of extinction and some general correlations between extinction curve shape and interstellar environment. These relationships provide some guidance for correcting data for the effects of extinction. Several strategies for dereddening are discussed along with estimates of the uncertainties inherent in each method. In the Appendix, a new derivation of the wavelength dependence of an average Galactic extinction curve from the IR through the UV is presented, along with a new estimate of how this extinction law varies with the parameter R≡A(V)/E(B−V). These curves represent the true monochromatic wavelength dependence of extinction and, as such, are suitable for dereddening IR–UV spectrophotometric data of any resolution and can be used to derive extinction relations for any photometry system.

view Abstract Citations (109) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The extragalactic distance scale. V. Tertiary distance indicators. de Vaucouleurs, G. Abstract A sample of 28 nearby galaxies whose distances were previously derived from five primary and four secondary distance indicators is used to calibrate the two main tertiary indicators: the isophotal diameters and the total magnitudes of the galaxies themselves, both fully corrected for galactic and internal extinction as well as redshift. The luminosity class of the DDO system and the morphological type of the revised Hubble system are combined into a composite luminosity index that is more closely correlated with absolute magnitude (or diameter) than either morphological type or luminosity class alone. This luminosity index is corrected for inclination effects and given for the calibrating galaxies, along with corrected isophotal diameters. The total magnitudes are reduced to face-on and corrected for galactic extinction and redshift. The zero points and their mean errors are determined, and the corresponding distance moduli are obtained. An error analysis shows that total magnitudes are better distance indicators than isophotal diameters. Publication: The Astrophysical Journal Pub Date: January 1979 DOI: 10.1086/156742 Bibcode: 1979ApJ...227..380D Keywords: Astrometry; Galactic Clusters; Interstellar Extinction; Luminous Intensity; Astronomical Photometry; Calibrating; Error Analysis; Red Shift; Astrophysics; Diameters:Galaxies; Distance Scale:Universe; Distances:Galaxies; Galaxies:Luminosities full text sources ADS | Related Materials (9) Part 1: 1978ApJ...223..351D Part 2: 1978ApJ...223..730D Part 3: 1978ApJ...224...14D Part 4: 1978ApJ...224..710D Part 6: 1979ApJ...227..729D Part 7: 1979ApJ...233..433D Part 8: 1982Obs...102..178D Part 9: 1983MNRAS.202..367D Part 10: 1993ApJ...415...10D