Interstellar Extinction Law Research Articles

The Optical to Infrared 0.6–5.3 μm Dust Extinction Law of the Milky Way with JWST NIRSpec: Westerlund 2

The interstellar extinction law is important for interpreting observations and inferring the properties of interstellar dust grains. Based on the 993 prism/CLEAR spectra from the James Webb Space Telescope (JWST), we investigate the 0.6–5.3 μm interstellar dust extinction law. We propose a pair method to obtain the reddening curves based only on JWST observed spectra. Most of the high-extinction sources are toward the young star cluster Westerlund 2. The infrared 1.0–5.3 μm reddening curves agree with the power law A λ ∝ λ −α well. We determine an average value of α = 1.98 ± 0.15, which is consistent with the average value of the Galaxy. We find that α may be variable and independent of R V . With the derived α, we convert the reddening curves into the extinction curves and establish the nonparameterized α-dependent extinction curves in the wavelength range of 0.6–5.3 μm. At λ < 1 μm, the derived extinction law is not well described by the parameterized power-law-type curve. Our nonparameterized α-dependent extinction curves are suitable for the extinction correction of JWST-based photometry and spectra measurements at 0.6–5.3 μm. We also provide the extinction coefficients for the JWST NIRCam bandpasses with different α.

The Optical to Infrared Extinction Law of Magellanic Clouds Based on Red Supergiants and Classical Cepheids

Precise interstellar dust extinction laws are important to infer the intrinsic properties of reddened objects and correctly interpret observations. In this work, we attempt to measure the optical–infrared extinction laws of the Large and Small Magellanic Clouds (LMC and SMC) by using red supergiant (RSG) stars and classical Cepheids as extinction tracers. The spectroscopic RSG samples are constructed based on the APOGEE spectral parameters, Gaia astrometric data, and multiband photometry. We establish the effective temperature–intrinsic color relations for RSG stars and determine the color excess ratio (CER) E(λ − G RP)/E(G BP − G RP) for the LMC and SMC. We use classical Cepheids to derive base relative extinction . The results are 1.589 ± 0.014 and 1.412 ± 0.041 for the LMC and SMC. By combining CERs with , the optical–infrared extinction coefficients are determined for 16 bands. We adjust the parameters of R V -dependent extinction laws and obtain average extinction laws for the LMC and SMC of R V = 3.40 ± 0.07 and R V = 2.53 ± 0.10, respectively, which are consistent with Gordon et al. In the optical bands, the adjusted R V extinction curves agree with the observations with deviations less than 3%.

A Deep Study of an Intermediate-age Open Cluster SAI 35 (Juchert 20) Using Ground-based Imaging and Gaia EDR3 Astrometry

Abstract We present a CCD UBVI photometric study of poorly studied intermediate-age open cluster SAI 35 (Juchert 20) for the first time. To accomplish this study, we also used LAMOST DR5, Two Micron All Sky Survey, and Gaia EDR3 databases. We identified 214 most probable cluster members with membership probability higher than 50%. The mean proper motion of the cluster is found as and μ δ = −1.66 ± 0.01 mas yr−1. We find the normal interstellar extinction law using the various two-color diagrams. The age, distance, reddening, and radial velocity of the cluster are estimated to be 360 ± 40 Myr, 2.9 ± 0.15 kpc, 0.72 ± 0.05 mag, and −91.62 ± 6.39 km s−1, respectively. The overall mass function slope for main-sequence stars is found to be 1.49 ± 0.16 within the mass range 1.1–3.1 M ⊙, which is in agreement with Salpeter’s value within uncertainty. The present study demonstrates that SAI 35 is dynamically relaxed. Galactic orbital parameters are determined using Galactic potential models. We found that this object follows a circular path around the Galactic center.

The study of the influence of interstellar extinction laws on the parameters of photometric system using astrophysical observations taken at EAO

In this work, connections between UBV (PSC UBV) photometric systems for various laws of interstellar extinction are calculated on the basis of digital database on astrophysical observations of Engelhardt astronomical observatory (EAO) and using the specialized software package for analyzing brightness characteristics. The following results are obtained: 1) when using various laws of interstellar extinction, the value of difference in the position of reaction curves is proportional to the difference between UBV dependencies and color indices; 2) the positions of reaction curves and connection curves between UBV and color indices are influenced by spectral characteristics of the filters used in observations; 3) the same applies to the transformation of stellar magnitudes from one standard system to another, as response curves as a rule significantly differ; 4) another conclusion is that for any separate model of interstellar extinction the differences in color between photometric systems do not depend on spectral and luminosity classes.

Stellar and interstellar parameters from large photometric surveys

The parameterization of stars is a well-known problem and used for various purposes in astronomy. We have shown that multicolor photometric data from large modern surveys can be used for parameterization of stars. With sufficiently good quality photometry, one may compute a 3D extinction map by comparing catalogued multicolor photometry with photometry derived from the secondary estimators such as the distance modulus and the interstellar extinction law with suitable calibration tables for absolute magnitudes with reasonable spectral types, extinctions and distances.

The Optical to Mid-infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS, and WISE Surveys

Abstract A precise interstellar dust extinction law is critically important to interpret observations. There are two indicators of extinction: the color excess ratio (CER) and the relative extinction. Compared to the CER, the wavelength-dependent relative extinction is more challenging to be determined. In this work, we combine spectroscopic, astrometric, and photometric data to derive high-precision CERs and relative extinction from optical to mid-infrared (IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by stellar parameters from the Apache Point Observatory Galaxy Evolution Experiment survey. The multiband photometric data are collected from Gaia, APASS, Sloan Digital Sky Survey, Pan-STARRS1, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer surveys. For the first time, we calibrate the curvature of CERs in determining CERs E(λ − G RP)/E(G BP − G RP) from color excess–color excess diagrams. Through elaborate uncertainty analysis, we conclude that the precision of our CERs is significantly improved (σ &lt; 0.015). With parallaxes from Gaia DR2, we calculate the relative extinction / for 5051 RC stars. By combining the CERs with the / , the optical–mid-IR extinction A λ / has been determined in a total of 21 bands. Given no bias toward any specific environment, our extinction law represents the average extinction law with the total-to-selective extinction ratio R V = 3.16 ± 0.15. Our observed extinction law supports an adjustment in parameters of the CCM R V = 3.1 curve, together with the near-IR (NIR) power-law index α = 2.07 ± 0.03. The relative extinction values of the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST) NIR bandpasses are predicted in 2.5% precision. As the observed reddening/extinction tracks are curved, the curvature correction needs to be considered when applying extinction correction.

Mass function and dynamical study of the open clusters Berkeley 24 and Czernik 27 using ground based imaging and Gaia astrometry

We present a $UBVI$ photometric study of the open clusters Berkeley 24 (Be 24) and Czernik 27 (Cz 27). The radii of the clusters are determined as 2\farcm7 and 2\farcm3 for Be 24 and Cz 27, respectively. We use the Gaia Data Release 2 (GDR2) catalogue to estimate the mean proper motions for the clusters. We found the mean proper motion of Be 24 as $0.35\pm0.06$ mas yr$^{-1}$ and $1.20\pm0.08$ mas yr$^{-1}$ in right ascension and declination for Be 24 and $-0.52\pm0.05$ mas yr$^{-1}$ and $-1.30\pm0.05$ mas yr$^{-1}$ for Cz 27. We used probable cluster members selected from proper motion data for the estimation of fundamental parameters. We infer reddenings $E(B-V)$ = $0.45\pm0.05$ mag and $0.15\pm0.05$ mag for the two clusters. Analysis of extinction curves towards the two clusters show that both have normal interstellar extinction laws in the optical as well as in the near-IR band. From the ultraviolet excess measurement, we derive metallicities of [Fe/H]= $-0.025\pm0.01$ dex and $-0.042\pm0.01$ dex for the clusters Be 24 and Cz 27, respectively. The distances, as determined from main sequence fitting, are $4.4\pm0.5$ kpc and $5.6\pm0.2$ kpc. The comparison of observed CMDs with $Z=0.01$ isochrones, leads to an age of $2.0\pm0.2$ Gyr and $0.6\pm0.1$ Gyr for Be 24 and Cz 27, respectively. In addition to this, we have also studied the mass function and dynamical state of these two clusters for the first time using probable cluster members. The mass function is derived after including the corrections for data incompleteness and field star contamination. Our analysis shows that both clusters are now dynamically relaxed

Red supergiant stars in the Large Magellanic Cloud

The characteristics of infrared properties and mid-infrared (MIR) variability of red supergiant (RSG) stars in the Large Magellanic Cloud (LMC) are analyzed based on 12 bands of near-infrared (NIR) to MIR co-added data from 2MASS, Spitzer and WISE, and ∼6.6 yr of MIR time-series data collected by the ALLWISE and NEOWISE-R projects. 773 RSGs candidates were compiled from the literature and verified by using the color-magnitude diagram (CMD), spectral energy distribution (SED) and MIR variability. About 15% of valid targets in the IRAC1–IRAC2/IRAC2–IRAC3 diagram may show polycyclic aromatic hydrocarbon (PAH) emission. We show that arbitrary dereddening Q parameters related to the IRAC4, S9W, WISE3, WISE4, and MIPS24 bands could be constructed based on a precise measurement of MIR interstellar extinction law. Several peculiar outliers in our sample are discussed, in which one outlier might be a RSG right before the explosion or an extreme asymptotic giant branch (AGB) star in the very late evolutionary stage based on the MIR spectrum and photometry. There are 744 identified RSGs in the final sample having both the WISE1- and WISE2-band time-series data. The results show that the MIR variability is increasing along with the increasing of brightness. There is a relatively tight correlation between the MIR variability, mass loss rate (MLR; in terms of KS–WISE3 color), and the warm dust or continuum (in terms of WISE4 magnitude/flux), where the MIR variability is evident for the targets with KS–WISE3 &gt; 1.0 mag and WISE4 &lt; 6.5 mag, while the rest of the targets show much smaller MIR variability. The MIR variability is also correlated with the MLR for which targets with larger variability also show larger MLR with an approximate upper limit of −6.1 M⊙ yr−1. Both the variability and the luminosity may be important for the MLR since the WISE4-band flux is increasing exponentially along with the degeneracy of luminosity and variability. The identified RSG sample has been compared with the theoretical evolutionary models and shown that the discrepancy between observation and evolutionary models can be mitigated by considering both variability and extinction.

Small Variation of the NIR and MIR Interstellar Extinction Laws

AbstractUsing the data from APOGEE, WISE, and GLIMPSE, we explored the variation of the near-infrared (NIR) and mid-infrared (MIR) interstellar extinction laws of the Milky Way. We derived the IR extinction laws towards a number of different sightlines, including 24 bins along Galactic latitude (b) and 592 plates observed by APOGEE. Our results indicate that E(J-H)/E(J-K) show only subtle variation along b, Galactic longitude (l), or the depth of E(J-K). This suggests that the NIR extinction law can be considered as universal. Similarly, E(K-W1, W2, W3, [3.6], [4.5], [5.8], [8.0])/E(J-K) also show only small variation along b, l, or the extinction depth. The MIR extinction curve is flat, indicating that the MIR extinction law is likely universal.

Bayesian approach to estimating stellar properties and interstellar extinction law based on photometry

We describe Bayesian probabilistic approach to estimating the properties of stars and the interstellar extinction law based on photometric observations and using prior data about the parameters of the stars. The accuracy of the resulting estimates is analyzed in the case of SDSS and 2MASS surveys. We found that our estimates have no systematic deviations in the case of photometric accuracy typical of the surveys considered and errors of prior data of ΔT eff = ±150 K and Δlog g = ±0.5. Note that the error of the estimated interstellar extinction A 0 is of about 0. m 3, and the error of the R 0 estimate depends on extinction and is close 0.2 for moderate A0 values. The fractional error of the estimated stellar angular diameters is close to 10%. A possible application of our approach is to determine the dependence of interstellar extinction on distance using stars closely located in the same sky area.

Dusty globules in the Crab Nebula

From existing broad-band images obtained with the Hubble Space Telescope, we located 92 globules, for which we derived positions, dimensions, orientations, extinctions, masses, proper motions, and their distributions. The globules have mean radii ranging from 400 to 2000 AU and are not resolved in current infrared images of the nebula. The extinction law for dust grains in these globules matches a normal interstellar extinction law. Derived masses of dust range from 1 to 60 x 10^(-6) solar masses, and the total mass contained in globules constitute a fraction of approximately 2% or less of the total dust content of the nebula. The globules are spread over the outer part of the nebula, and a fraction of them coincide in position with emission filaments, where we find elongated globules that are aligned with these filaments. Only 10% of the globules are coincident in position with the numerous H2-emitting knots found in previous studies. All globules move outwards from the centre with transversal velocities of 60 to 1600 km/s, along with the general expansion of the remnant. We discuss various hypotheses for the formation of globules in the Crab Nebula.

TOWARD UNDERSTANDING THE B[e] PHENOMENON. VI. NATURE AND SPECTRAL VARIATIONS OF HD 85567∗

Abstract We report the results of high-resolution (R ∼ 80,000) spectroscopic observations of the emission-line object HD 85567, which has been classified as an FS CMa type object or a pre-main-sequence star. The main goal is to put more constraints on the object’s fundamental parameters, as well as on its nature and evolutionary state. Absorption lines in the spectrum of HD 85567 were found to be similar to those of mid-B-type dwarfs and correspond to the following fundamental parameters: T eff = 15,000 ± 500 K, km s−1, and . The interstellar extinction, A V = 0.50 ± 0.02 mag, was measured using the strengths of some diffuse interstellar bands. We also obtained UBV(RI)c images of a 10′ × 10′ region around the object. Photometry of projectionally close stars was used to derive an interstellar extinction law in this direction and resulted in a distance of 1300 ± 100 pc to the object and a luminosity of log L/L ⊙ = 3.3 ± 0.2. We found no significant radial velocity variations of the absorption lines in the spectra of HD 85567 obtained during two-month-long periods of time in 2012 and 2015. Our analysis of the spectroscopic and photometric data available for the star led us to a conclusion that it cannot be a pre-main-sequence Herbig Ae/Be star. We argue that the circumstellar gas and dust were produced during the object’s evolution as most likely a binary system, which contains an undetected secondary component and is unlikely to be a merger product.

Interstellar Extinction in 20 Open Star Clusters

AbstractThe interstellar extinction law in 20 open star clusters namely, Berkeley 7, Collinder 69, Hogg 10, NGC 2362, Czernik 43, NGC 6530, NGC 6871, Bochum 10, Haffner 18, IC 4996, NGC 2384, NGC 6193, NGC 6618, NGC 7160, Collinder 232, Haffner 19, NGC 2401, NGC 6231, NGC 6823, and NGC 7380 have been studied in the optical and near-IR wavelength ranges. The difference between maximum and minimum values of E(B − V) indicates the presence of non-uniform extinction in all the clusters except Collinder 69, NGC 2362, and NGC 2384. The colour excess ratios are consistent with a normal extinction law for the clusters NGC 6823, Haffner 18, Haffner 19, NGC 7160, NGC 6193, NGC 2401, NGC 2384, NGC 6871, NGC 7380, Berkeley 7, Collinder 69, and IC 4996. We have found that the differential colour-excess ΔE(B − V), which may be due to the occurrence of dust and gas inside the clusters, decreases with the age of the clusters. A spatial variation of colour excess is found in NGC 6193 in the sense that it decreases from east to west in the cluster region. For the clusters Berkeley 7, NGC 7380, and NGC 6871, a dependence of colour excess E(B − V) with spectral class and luminosity is observed. Eight stars in Collinder 232, four stars in NGC 6530, and one star in NGC 6231 have excess flux in near-IR. This indicates that these stars may have circumstellar material around them.

Extinction law at a distance up to 25 kpc toward the Galactic poles

Photometry from the Tycho-2, 2MASS, and WISE catalogues for clump and branch giants at a distance up to 25 kpc toward the Galactic poles has allowed the variations of various characteristics of the infrared interstellar extinction law with distance to be analyzed. The results obtained by the extinction law extrapolation method are consistent for different classes of stars and different characteristics as well as with previous studies. The conventional extinction law with a low infrared extinction is characteristic of only a thin layer no farther than 100 pc from the Galactic plane and of two thin layers near $Z=-600$ and $+500$ pc. Far from the Galactic plane, in the Galactic halo, the infrared extinction law is different: the extinction in the $Ks$, $W1$, $W2$, $W3$, and $W4$ bands is, respectively, $0.17$, $0.16$, $0.16$, $0.07$, and $0.03$ of the extinction in the $V$ band. The accuracy of these coefficients is $0.03$. If the extinction law reflects primarily the grain size distribution, then the fraction of large dust grains far from the Galactic plane is greater than that in the circumsolar interstellar medium.

A PRECISE DETERMINATION OF THE MID-INFRARED INTERSTELLAR EXTINCTION LAW BASED ON THE APOGEE SPECTROSCOPIC SURVEY

ABSTRACT A precise measure of the mid-infrared interstellar extinction law is crucial for investigating the properties of interstellar dust, especially larger-sized grains. Based on the stellar parameters derived from the SDSS-III/Apache Point Observatory Galaxy Evolution Experiment (APOGEE) spectroscopic survey, we select a large sample of G-type 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 extinctions (relative to , the K S-band extinction at wavelength λ = 2.16 μm) for the four Wide-field Infrared Survey Explorer (WISE) bands at 3.4, 4.6, 12, and 22 μm, the four Spitzer/Infrared Array Camera bands at 3.6, 4.5, 5.8, and 8 μm, the Spitzer/MIPS24 band at 23.7 μm, and, for the first time, the AKARI/S9W band at 8.23 μm. Our results agree with previous works in that the extinction curve is flat in the ∼3–8 μm wavelength range and is generally consistent with the = 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 , 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.

Photometric study of open star clusters in II quadrant: Teutsch 1 and Riddle 4

We present the broad band UBVI CCD photometry in the region of two open star clusters Teutsch 1 and Riddle 4 located in the second Galactic quadrant. The optical CCD data for these clusters are obtained for the first time. Radii of the clusters are estimated as 3′.5 for both the clusters. Using two color (U−B) versus (B−V) diagram we determined the reddening as E(B−V)=0.40± 0.05 mag for Teutsch 1 and 1.10 ± 0.05 mag for Riddle 4. Using 2MASS JHK and optical data, we estimated E(J−K)=0.24± 0.05 mag and E(V−K)=1.40± 0.05 mag for Teutsch 1 and E(J−K)=0.47± 0.06 mag and E(V−K)=2.80± 0.06 mag for Riddle 4. Color-excess ratio indicates normal interstellar extinction law in the direction of both the clusters. We estimated distance as 4.3 ± 0.5 Kpc for Teutsch 1 and 2.8 ± 0.2 Kpc for Riddle 4 by comparing the color-magnitude diagram of the clusters with theoretical isochrones. The age of the clusters has been estimated as 200 ± 20 Myr for Teutsch 1 and 40 ± 10 Myr for Riddle 4 using the stellar isochrones of metallicity Z=0.02. The Mass function slope has been derived 1.89 ± 0.43 and 1.41 ± 0.70 for Teutsch 1 and Riddle 4 respectively. Our analysis indicates that both the clusters are dynamically relaxed. A slight bend of Galactic disc towards the southern latitude is found in the longitude range l= 130–180°.

Classification of stars with WBVR photometry

AbstractWe present a method of obtaining the most reliable stellar spectral type based on multi‐color photometry. The method also allows us to estimate color excess EB—V and distance to the star. Approbation of the method using bright stars with known spectral classification and WBVR photometry permits to estimate its reliability. Stellar spectra models from Pickles (1998) library and Fluks et al. (1994) interstellar extinction law were used in the application of the method. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Photometric studies of open star clusters Haffner 11 and Czernik 31

We present the broad band UBVI CCD photometric investigations in the region of the two open clusters Haffner 11 and Czernik 31. The radii of the clusters are determined as 3′.5 and 3′.0 for Haffner 11 and Czernik 31 respectively. Using two colour (U-B) versus (B-V) diagram we determine the reddening E(B-V)=0.50±0.05mag and 0.48±0.05mag for the cluster Haffner 11 and Czernik 31 respectively. Using 2MASS JHKs and optical data, we determined E(J-K)=0.27±0.06mag and E(V-K)=1.37±0.06 for Haffner 11 and E(J-K)=0.26±0.08mag and E(V-K)=1.32±0.08 mag for Czernik 31. Our analysis indicate normal interstellar extinction law in the direction of both the clusters. Distance of the clusters is determined as 5.8±0.5Kpc for Haffner 11 and 3.2±0.3Kpc for Czernik 31 by comparing the ZAMS with the CM diagram of the clusters. The age of the cluster has been estimated as 800±100 Myr for Haffner 11 and 160±40Myr for Czernik 31 using the stellar isochrones of metallicity Z=0.019.

Spatial variations of the extinction law in the galactic disk from infrared observations

Infrared photometry in the J (1.2 microns), H (1.7 microns), Ks (2.2 microns) bands from the 2MASS catalogue and in the W1 (3.4 microns), W2 (4.6 microns), W3 (12 microns), W4 (22 microns) bands from the WISE catalogue is used to reveal the spatial variations of the interstellar extinction law in the infrared near the midplane of the Galaxy by the method of extrapolation of the extinction law applied to clump giants. The variations of the coefficients E(H-W1)/E(H-Ks), E(H-W2)/E(H-Ks), E(H-W3)/E(H-Ks), and E(H-W4)/E(H-Ks) along the line of sight in 2 deg per 2 deg squares of the sky centered at b=0 and l=20, 30, ..., 330, 340 deg as well as in several 4 deg per 4 deg squares with |b|=10 are considered. The results obtained here agree with those obtained by Zasowski et al. in 2009 using 2MASS and Spitzer-IRAC photometry for the same longitudes and similar photometric bands, confirming their main result: in the inner (relative to the Sun) Galactic disk, the fraction of fine dust increases with Galactocentric distance (or the mean dust grain size decreases). However, in the outer Galactic disk that was not considered by Zasowski et al., this trend is reversed: at the disk edge, the fraction of coarse dust is larger than that in the solar neighborhood. This general Galactic trend seems to be explained by the influence of the spiral pattern: its processes sort the dust by size and fragment it so that coarse and fine dust tend to accumulate, respectively, at the outer and inner (relative to the Galactic center) edges of the spiral arms. As a result, fine dust may exist only in the part of the Galactic disk far from both the Galactic center and the edge, while coarse dust dominates at the Galactic center, at the disk edge, and outside the disk.

ON ABSORPTION BY CIRCUMSTELLAR DUST, WITH THE PROGENITOR OF SN 2012aw AS A CASE STUDY

ABSTRACT 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 &lt; L */L ☉ &lt; 105.0 and the star was not extremely massive for a Type IIP progenitor, with M * &lt; 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.