Wavelength Dependence Of Interstellar Extinction Research Articles

PIETER JOHANNES VAN RHIJN, KAPTEYN'S ASTRONOMICAL LABORATORY AND THE <italic>PLAN OF SELECTED AREAS</italic>

In this paper I discuss the Kapteyn Astronomical Laboratory during the period of Pieter Johannes van Rhijn's Directorate, which lasted from 1921 to 1957. It had developed under the founder Jacobus Cornelius Kapteyn into one of the leading astronomical research institutes in the world. When van Rhijn took over at the retirement of Kapteyn, it was in the process of coordinating Kapteyn's <italic>Plan of Selected Areas</italic> with the aim of determining the structure of the Sidereal System. Kapteyn had just, with the help of van Rhijn, presented a first model of the distribution of stars in space from existing observations, and on this basis he constructed a 'first attempt' model of the Stellar System including dynamics, i.e. deriving the gravitational field from the distribution of the stars and showing how the random and systematic motions of the stars, the kinematics, could provide equilibrium and stability to the system. Under van Rhijn, the work on the <italic>Selected Areas</italic> progressed well, but the Groningen Laboratorium went into decline, loosing much of its status and prestige. I conclude the following. There was very little choice for Kapteyn's successor and van Rhijn was appointed effectively by default. Kapteyn himself must have seen that the future for astronomy in the Netherlands lay with Leiden Observatory, where already during his lifetime two of his protégées, Willem de Sitter and Ejnar Hertzsprung, were in charge, and to which a third one was added not much later in the person of Jan Oort. Kapteyn had his <italic>Plan of Selected Areas</italic> in addition to the scientific case set up as a way of ensuring the future of the Groningen Laboratorium at least for the time of this effort, arranging it to be supplied with plate material to complete the provision of the data for the final attack on the Sidereal problem. Van Rhijn's research was solid and professional, but in his papers he invariably stopped before discussing how his findings fitted into the larger emerging picture of the structure of the Galaxy. Comparison of his work in the 1930s on the distribution of stars as a function of spectral types and Jan Hendrik Oort's determination of his 1938 crosscut through the Galaxy illustrates this. While this work by Oort constituted the second attempt following on Kapteyn's first, and may be seen as the actual completion of the research for which the <italic>Plan of Selected Areas</italic> was designed, van Rhijn continued adding more and more data in the context of the Plan without redefining the aims in the light of developments. The <italic>Spectral Durchmusterung</italic> carried out in collaboration with the Bergedorf-Hamburg Sternwarte and Harvard College Observatory was an enormous drain on the Groningen resources. Van Rhijn's successful attempt to obtain his own telescope resulted in very relevant and correct determinations of the wavelength dependence of interstellar extinction from photographic spectra, but these results only became available in the 1950s when the field had turned to photoelectric methods. Kapteyn's concept of an astronomical laboratory lost its viability in van Rhijn's time when observa-tories were no longer interested in providing observational material for others to do research. Kapteyn's model on the other hand of a laboratory-like institution, where research is based on material obtained elsewhere on Earth or in space, is now the normal operating mode in astronomical research. The only difference is access to observing facilities primarily, which is now structured and guaranteed (subject to proposal acceptance of course), through national and international organizations rather than access on the basis of one's fame or stature. The cause of the loss of the Kapteyn Laboratorium of its prominent place in the international context was largely van Rhijn's unwavering dedication to complete Kapteyn's work. The <italic>Plan of Selected Areas</italic> had been important for the progress of astronomy, but effectively reached the goals Kapteyn had in mind for it already in the 1930s with Oort's 1932 work on the vertical force field and local 'Oort limit' and his 1938 crosscut through the Galaxy. Van Rhijn was unfortunately hampered throughout almost his entire Directorate by factors that severely limited his attempts to obtain more funding in spite of local support from his university. These were of course in the first place the Great Depression of the 1930s and World War II and its aftermath, while during most of the 1940s he suffered from tuberculosis. But, also, the remote location of Groningen compared to Leiden, where a major infrastructure led by three important protégées of Kapteyn was in place, and the Governmental bias towards support for Leiden over Groningen was an important factor. Finally, I examine the developments in the 1950s and the circumstances that made Adriaan Blaauw accept his appointment as van Rhijn's successor in 1957 and initiate the beginnings of the revival of the Kapteyn Laboratorium under his leadership.

NEW ULTRAVIOLET EXTINCTION CURVES FOR INTERSTELLAR DUST IN M31

New low-resolution UV spectra of a sample of reddened OB stars in M31 were obtained with HST/STIS to study the wavelength dependence of interstellar extinction and the nature of the underlying dust grain populations. Extinction curves were constructed for four reddened sightlines in M31 paired with closely matching stellar atmosphere models. The new curves have a much higher S/N than previous studies. Direct measurements of N(H I) were made using the Ly$\alpha$ absorption lines enabling gas-to-dust ratios to be calculated. The sightlines have a range in galactocentric distance of 5 to 14 kpc and represent dust from regions of different metallicities and gas-to-dust ratios. The metallicities sampled range from Solar to 1.5 Solar. The measured curves show similarity to those seen in the Milky Way and the Large Magellanic Cloud. The Maximum Entropy Method was used to investigate the dust composition and size distribution for the sightlines observed in this program finding that the extinction curves can be produced with the available carbon and silicon abundances if the metallicity is super-Solar.

THE MID-INFRARED EXTINCTION LAW AND ITS VARIATION IN THE COALSACK NEBULA

In recent years the wavelength dependence of interstellar extinction from the ultraviolet (UV), optical, through the near- and mid-infrared (IR) has been studied extensively. Although it is well established that the UV/optical extinction law varies significantly among the different lines of sight, it is not clear how the IR extinction varies among various environments. In this work, using the color-excess method and taking red giants as the extinction tracer, we determine the interstellar extinction Alambda in the four Spitzer/IRAC bands of the Coalsack nebula, a nearby starless dark cloud, based on the data obtained from the 2MASS and Spitzer/GLIMPSE surveys. We select five individual regions across the nebula that span a wide variety of physical conditions, ranging from diffuse, translucent to dense environments, as traced by the visual extinction, the Spitzer/MIPS 24micron emission, and CO emission. We find that Alambda/AKs, the mid-IR extinction relative to AKs, decreases from diffuse to dense environments, which may be explained in terms of ineffective dust growth in dense regions. The mean extinction (relative to AKs) is calculated for the four IRAC bands as well, which exhibits a flat mid-IR extinction law, consistent with previous determinations for other regions. The extinction in the IRAC 4.5micron band is anomalously high, much higher than that of the other three IRAC bands. It cannot be explained in terms of CO and CO2 ices. The mid-IR extinction in the four IRAC bands have also been derived for four representative regions in the Coalsack Globule 2 which respectively exhibit strong ice absorption, moderate or weak ice absorption, and very weak or no ice absorption. The derived mid-IR extinction curves are all flat, with Alambda/AKs increasing with the decrease of the H2O ice absorption optical depth.

Optical polarimetric study of open clusters: distribution of interstellar matter towards NGC 654

ABSTRACT We present new B,V and R linear polarimetric observations for 61 starstowards the region of the young open cluster NGC 654. In this study we foundevidence for the presence of at least two layers of dust along the line of sight tothe cluster. The distances to the two dust layers are estimated to be ∼ 200 pcand ∼ 1 kpc which are located much closer to the Sun than the cluster (∼ 2.4kpc). Both the dust layers have their local magnetic field orientation nearlyparallel to the direction of the Galactic plane. The foreground dust layer isfound to have a ring morphology with the central hole coinciding with thecenter of the cluster. The foreground dust grains are suggested to be mainlyresponsible for both the observed differential reddening and the polarizationtowards the cluster.Keywords: polarization-dust, extinction-openclustersandassociations:individual:NGC 654 1 INTRODUCTIONThe wavelength dependence of interstellar extinction and polarization provides constraintson the characteristics of interstellar grains. Interstellar polarization strongly varies withwavelength (Serkowski, Mathewson & Ford 1975; Wilking et al. 1980). In particular, thewavelength of maximum interstellar polarization (λ

Reddening and the Extinction Law at High Galactic Latitude

We present near-infrared (JHKL) photometry of 103 southern stars located behind translucent interstellar clouds at high Galactic latitude. Our data are combined with visual photometry and spectral type information from the literature in a detailed analysis of the wavelength dependence of interstellar extinction by dust in these high-latitude clouds. We investigate the shape of the near-infrared extinction curve and evaluate the total line-of-sight extinction (AV) and ratio of total-to-selective extinction (RV) in each line of sight. Sources of uncertainty in RV arising from photometric errors and spectral classification errors are carefully assessed and quantified as functions of the line-of-sight reddening. We detect appreciable differences in our results compared with the average extinction curve for dust in the diffuse interstellar medium (ISM) close to the Galactic plane. Assuming a power-law form in the near-infrared, we find the mean for high-latitude clouds to be well described by Aλ ∝ λ-2.3, somewhat steeper than that for the diffuse ISM (Aλ ∝ λ-1.8). Our sample includes a substantial number of lines of sight with low RV values (47% with RV < 2.8) relative to the diffuse ISM average of 3.05 ± 0.15. We conclude that many high-latitude clouds have enhanced abundances of relatively small grains.

The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 μm Using GLIMPSE Data

We determine and tabulate A[λ]/AK, the wavelength dependence of interstellar extinction, in the Galactic plane for 1.25 μm ≤ λ ≤ 8.0 μm along two lines of sight: l = 42° and 284°. The first is a relatively quiescent and unremarkable region; the second contains the giant H II region RCW 49, as well as a field region unrelated to the cluster and nebulosity. Areas near these Galactic longitudes were imaged at J, H, and K bands by 2MASS and at 3-8 μm by Spitzer for the GLIMPSE Legacy program. We measure the mean values of the color excess ratios (A[λ] - AK)/(AJ - AK) directly from the color distributions of observed stars. The extinction ratio between two of the filters, e.g., AJ/AK, is required to calculate A[λ]/AK from those measured ratios. We use the apparent JHK magnitudes of giant stars along our two sight lines and fit the reddening as a function of magnitude (distance) to determine AJ kpc-1, AK kpc-1, and AJ/AK. Our values of A[λ]/AK show a flattening across the 3-8 μm wavelength range, roughly consistent with the extinction measurements derived by Lutz and coworkers for the sight line toward the Galactic center.

Fundamental absorption in solids and the wavelength dependence of interstellar extinction

It is found that the wavelength dependence of interstellar extinction between the 0.44-μm band and 8 μm follows a Tauc-Urbach law characteristic of amorphous semiconductors. This result implies that the majority of extinction in this wavelength range arises predominantly from an amorphous dust component. A comparison betwen laboratory and interstellar data suggests that this dust is likely to be amorphous carbon. The Tauc-Urbach dependence permits the ratio of total to selective extinction, R V , to be related to the optical properties of this dust component and provides a semiquantitative relation between R V and environmental conditions in the interstellar medium

Interstellar Extinction in External Galaxies

In this paper I review the existing measurements of the wavelength dependence of interstellar extinction arising from dust situated outside the Milky Way galaxy. This paper emphasizes studies of extinction in the Large and Small Magellanic Clouds. I discuss the UV extinction properties, as well as the optical and near-IR properties as determined from ground-based photometry.

Polymeric complexes in comets and in space

A distribution of fluffy polymeric aggregates similar to that found in the dust from Comet Halley, together with and admixture of free polymers and graphite, leads to a close agreement with the observed wavelength dependence of interstellar extinction.

Vector space methods of photometric analysis. II - Refinement of the MK grid for B stars. III - The two components of ultraviolet reddening

This paper discusses systematic errors which arise from exclusive use of the MK system to determine reddening. It is found that implementation of uvby, beta photometry to refine the qualitative MK grid substantially reduces stellar mismatch error. A working definition of 'identical' ubvy, beta types is investigated and the relationship of uvby to B-V color excesses is determined. A comparison is also made of the hydrogen based uvby, beta types with the MK system based on He and metal lines. A small core correlated effective temperature luminosity error in the MK system for the early B stars is observed along with a breakdown of the MK luminosity criteria for the late B stars. The second part investigates the wavelength dependence of interstellar extinction in the ultraviolet wavelength range observed with the TD-1 satellite. In this study the sets of identical stars employed to find reddening are determined more precisely than in previous studies and consist only of normal, nonsupergiant stars. A multivariate analysis of variance techniques in an unbiased coordinate system is used for determining the wavelength dependence of reddening.

The Interstellar Radiation Density Between 1250 and 4250 A

view Abstract Citations (150) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Interstellar Radiation Density Between 1250 and 4250 A Witt, Adolf N. ; Johnson, Michael W. Abstract Using a model distribution of stars and dust, we have calculated the interstellar radiation density in the solar vicinity. The detailed wavelength dependence of interstellar extinction and of the albedo of the interstellar grains was taken into account, and the transformation of the stellar luminosity function was based on OAO-2 photometry. We find excellent agreement between our calculations and empirical data determined by Lillie, but we predict a radiation density h;gher by about a factor of two compared to earlier calculations by Habing for the wavelength range from 1000 to 2000 A. We also find a very steep rise in the spectrum of the radiation field toward shorter wavelengths in the interval 500 A. This rise, if characteristic for galaxies in general, may in part explain the high ultraviolet fluxes observed from galaxies with OAO-2. The revised shape of the spectrum of the interstellar radiation field is expected to be of consequence in studies of the ionization equilibrium of interstellar clouds. Subject headings: interstellar matter - ultraviolet Publication: The Astrophysical Journal Pub Date: April 1973 DOI: 10.1086/152054 Bibcode: 1973ApJ...181..363W full text sources ADS |

Interstellar Polarization

A review of observational data on interstellar polarization is given. The degree of fluctuation in the direction of the galactic magnetic field is discussed. An empirical formula is given which fits all the observations of the wavelength dependence of interstellar polarization when they are normalized with the wavelength λmax of maximum polarization. Well-defined regions on the sky with values of λmax deviating from an average are found. Values of λmax are correlated with the ratio of total to selective interstellar extinction. A unified wavelength dependence of interstellar extinction is obtained by normalizing the observations with the wavelength λmax of maximum interstellar polarization.

Polarization-wavelength Profile of the Interstellar 4430 Å Absorption Band

KNOWLEDGE of the scattering and polarizing properties of interstellar grains has now reached the stage where very specific models are being proposed for the composition and size distribution of these grains. It is evident that high resolution studies of the wavelength dependence of interstellar extinction and polarization will provide important tests of the proposed grain models. Although much work has been done on detailed studies of interstellar extinction, the detailed wavelength dependence of interstellar polarization at a higher resolution needs more study. Another related problem concerns the possibility that the diffuse interstellar bands, the most intense of which occurs at 4430 A, may be polarized differently from the neighbouring continuum: the amount and nature of this difference, if any, may give a clue to their origin. Spectrophotometry of these bands is always difficult because of the width and shallowness of the features, and polarization studies are correspondingly more difficult. By the use of a Wollaston prism at the Cassegrain focus of the 36-inch telescope of the Royal Observatory, Edinburgh, we have been able to derive a polarization profile across the 4430 band. This report describes the method and presents the preliminary results.

Correlation Between the Regional Variations in Wavelength Dependence of Interstellar Extinction and Polarization

Correlation Between the Regional Variations in Wavelength Dependence of Interstellar Extinction and Polarization

Photometric and Polarimetric Observations of the Nearby Strongly Reddened Open Cluster STOCK 2

view Abstract Citations (49) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric and Polarimetric Observations of the Nearby Strongly Reddened Open Cluster Stock 2 Krzeminski, W. ; Serkowski, K. Abstract Photoelectric UB V observations are given for 172 stars in the region of the cluster Stock 2 (iTi = 133 , = - 1?7) along with polarimetric observations for 127 stars. The distance modulus corrected for ab- sorption is 7 50 (r = 316 pc), and the mean reddening = 0 375 mag. The bluest cluster members are of spectral type B9; the color-magnitude diagram is similar to that of M11. The cluster membership of four red giants with -1 <Mv < +1 is confirmed by polarimetric and proper-motion data. The slope of the reddening path ! varies from 0 74 to 0 82 for the main-sequence stars with (B - V)8 between +004 and +032. The UB VRI observations of 10 cluster members indicate that in this spectral region the wavelength dependence of interstellar extinction is similar to that observed in Cygnus and Cepheus. The variable-extinction method applied to the cluster members with +020< (B - V)8 < +040 gives the ratio of total to selective interstellar extinction R = 3 4 + 0 1 only slightly larger than that for h and x Persei; the latter clusters are situated only 2?4 south of Stock 2 but are several times farther away The mean amount of polarization for the cluster members is 0.050 mag; the polarization is not correlated with reddening. The microscale 0 3 pc is found for the fluctuations in the polarizing medium. Publication: The Astrophysical Journal Pub Date: March 1967 DOI: 10.1086/149089 Bibcode: 1967ApJ...147..988K full text sources ADS | data products SIMBAD (173) GCPD (1)

The Wavelength Dependence of Interstellar Extinction

view Abstract Citations (101) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Wavelength Dependence of Interstellar Extinction Whiteoak, J. B. Abstract The law of interstellar extinction between wavelengths 3448 and 10500 A has been investigated in five regions of the Milky Way, namely, in Perseus, Orion, Monoceros, Cygnus, and Cepheus. Reddened and virtually unreddened stars of early spectral types were observed at thirty wavelengths with a photoelectric spectrum scanner at Mount Wilson. By adoption of theoretical models for unreddened energy distributions, the mean wavelength dependence of interstellar extinction was calculated for each region. The results for Perseus and Cepheus are similar. In Orion, the wavelength dependence for stars outside the Orion Nebula is different from the dependence within the nebula. The law for Monoceros lies between that for Orion and those of the remaining regions. There is no correlation between the results and galactic structure. Publication: The Astrophysical Journal Pub Date: April 1966 DOI: 10.1086/148605 Bibcode: 1966ApJ...144..305W full text sources ADS |

Some Observational Limitations of Extinction Measurements in the Rocket Ultraviolet

Even Before any Measurement of stellar fluxes in the ultraviolet had been obtained, predictions were being made on the basis of stellar atmosphere models. At the moment, it seems that such com-putations (for example, see ref. 1) are in reasonable agreement with actual observations from rockets (ref. 2) in the spectral region down to about 2000 Å. At shorter wavelengths it is necessary to take into account the appreciable blanketing by spectral lines which unavoidably is present in the transmission bands of any wide-band photometric system, even in the case of early B stars, as has been shown in reference 3.It must be anticipated that the reduction of extinction measurements in the UV from spaceborne instruments will follow the same procedure that has been used so far: stars with the same intrinsic energy distribution but with different amounts of reddening material in the line of sight are compared, the difference in energy distribution being attributed to the wavelength dependence of interstellar extinction.