A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves

We present an exhaustive, quantitative comparison of all of the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior of Milky Way extinction curves. The R_V dependent CCM relationship and the sample of extinction curves used to derive this relationship is used to describe the general behavior of Milky Way extinction curves. The ultraviolet portion of the SMC and LMC extinction curves are derived from archival IUE data, except for one new SMC extinction curve which was measured using HST/STIS observations. The optical extinction curves are derived from new (for the SMC) and literature UBVRI photometry (for the LMC). The near-infrared extinction curves are calculated mainly from 2MASS photometry supplemented with DENIS and new JHK photometry. For each extinction curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust column as the extinction curve. We compare the properties of the SMC and LMC extinction curves with the CCM relationship three different ways: each curve by itself, the behavior of extinction at different wavelengths with R_V, and behavior of the extinction curve FM fit parameters with R_V. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship, but majority of the LMC and all of the SMC curves do not follow the CCM relationship. For the first time, we find that the CCM relationship seems to form a bound on the properties of all of the LMC and SMC extinction curves. This result strengthens the picture of dust extinction curves exhibit a continuum of properties between those found in the Milky Way and the SMC Bar. (abridged)Comment: 18 pages, 10 figures, ApJ in pres

Correcting for the Effects of Interstellar Extinction

This 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.Comment: To appear in PASP (January 1999) 14 pages including 4 pages of figures Uses emulateapj style. PASP, in press (January 1999

Partial extinction and reinstatement

Fear extinction is not permanent but more vulnerable than the original fear memory, as relapse phenomena have traditionally shown. Partial extinction has been proposed as a strategy that may serve to mitigate relapses. Partial extinction differs from the standard procedure as it includes the occasional presentation of CS-US trials at the beginning of the extinction training. The present experiment, using an aversive differential conditioning procedure, evaluates whether partial extinction can reduce reinstatement, a specific form of relapse. The results showed that partial extinction did not mitigate reinstatement but proved effective to diminish the magnitude of the US expectation after a first reacquisition trial in a final test phase. The results reported are more consistent with theories that conceives extinction as the acquisition of new inhibitory learning rather than the erasure of the original conditioning.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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.Comment: 39 pages, 13 figures, accepted by Ap

The 2200 A bump and the UV extinction curve

The 2200 A bump is a major figure of interstellar extinction. Extinction curves with no bump however exist and are, with no exception, linear from the near-infrared down to 2500 A at least, often over all the visible-UV spectrum. The duality linear versus bump-like extinction curves can be used to re-investigate the relationship between the bump and the continuum of interstellar extinction, and answer questions as why do we observe two different kinds of extinction (linear or with a bump) in interstellar clouds? How are they related? How does the existence of two different extinction laws fits with the requirement that extinction curves depend exclusively on the reddening E(B-V) and on a single additional parameter? What is this free parameter? It will be found that (1) interstellar dust models, which suppose the existence of three different types of particles, each contributing to the extinction in a specific wavelength range, fail to account for the observations; (2) the 2200 A bump is very unlikely to be absorption by some yet unidentified molecule; (3) the true law of interstellar extinction must be linear from the visible to the far-UV, and is the same for all directions, including other galaxies. In extinction curves with a bump the excess of starlight (or the lack of extinction) observed at wavelengths less than lambda=4000 A is due to a large contribution of light scattered by hydrogen on the line of sight. Although counter-intuitive this contribution is predicted by theory. The free parameter of interstellar extinction is related to distances between the observer, the cloud on the line of sight, and the star behind it (the parameter is likely to be the ratio of the distances from the cloud to the star and to the observer). The continuum of the extinction curve or the bump contain no information concerning the chemical composition of interstellar cloud.Comment: 10 pages, 2 figure

The Optical -- Mid-infrared Extinction Law of the l=165 Sightline in the Galactic Plane: Diversity of Extinction Law in the Diffuse Interstellar Medium

Understanding the effects of dust extinction is important to properly interpret observations. The optical total-to-selective extinction ratio, Rv = Av/E(B-V), is widely used to describe extinction variations in ultraviolet and optical bands. Since the Rv=3.1 extinction curve adequately represents the average extinction law of diffuse regions in the Milky Way, it is commonly used to correct observational measurements along sightlines toward diffuse regions in the interstellar medium. However, the Rv value may vary even along different diffuse interstellar medium sightlines. In this paper, we investigate the optical--mid-infrared (mid-IR) extinction law toward a very diffuse region at l = 165 in the Galactic plane, which was selected based on a CO emission map. Adopting red clump stars as extinction tracers, we determine the optical-to-mid-IR extinction law for our diffuse region in the two APASS bands (B, V), the three XSTPS-GAC bands (g, r, i), the three 2MASS bands (J, H, Ks, and the two WISE bands (W1, W2). Specifically, 18 red clump stars were selected from the APOGEE--RC catalog based on spectroscopic data in order to explore the diversity of the extinction law. We find that the optical extinction curves exhibit appreciable diversity. The corresponding Rv ranges from 1.7 to 3.8, while the mean Rv value of 2.8 is consistent with the widely adopted average value of 3.1 for Galactic diffuse clouds. There is no apparent correlation between Rv value and color excess E(B-V) in the range of interest, from 0.2 to 0.6 mag, or with specific visual extinction per kiloparsec, AV/d.Comment: 28 pages, 7 figures, accepted for publication in The Astrophysical Journa

Decline in extinction rates and scale invariance in the fossil record

We show that the decline in the extinction rate during the Phanerozoic can be accurately parameterized by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results which previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.Comment: 11 pages including 3 postscript figures, typeset in LaTeX 2e using the Elsevier macro package elsart.cl

Environmental enrichment facilitates cocaine-cue extinction, deters reacquisition of cocaine self-administration and alters AMPAR GluA1 expression and phosphorylation

This study investigated the combination of environmental enrichment (EE) with cocaine‐cue extinction training on reacquisition of cocaine self‐administration. Rats were trained under a second‐order schedule for which responses were maintained by cocaine injections and cocaine‐paired stimuli. During three weekly extinction sessions, saline was substituted for cocaine but cocaine‐paired stimuli were presented. Rats received 4‐h periods of EE at strategic time points during extinction training, or received NoEE. Additional control rats received EE or NoEE without extinction training. One week later, reacquisition of cocaine self‐administration was evaluated for 15 sessions, and then GluA1 expression, a cellular substrate for learning and memory, was measured in selected brain regions. EE provided both 24 h before and immediately after extinction training facilitated extinction learning and deterred reacquisition of cocaine self‐administration for up to 13 sessions. Each intervention by itself (EE alone or extinction alone) was ineffective, as was EE scheduled at individual time points (EE 4 h or 24 h before, or EE immediately or 6 h after, each extinction training session). Under these conditions, rats rapidly reacquired baseline rates of cocaine self‐administration. Cocaine self‐administration alone decreased total GluA1 and/or pSer845GluA1 expression in basolateral amygdala and nucleus accumbens. Extinction training, with or without EE, opposed these changes and also increased total GluA1 in ventromedial prefrontal cortex and dorsal hippocampus. EE alone increased pSer845GluA1 and EE combined with extinction training decreased pSer845GluA1 in ventromedial prefrontal cortex. EE might be a useful adjunct to extinction therapy by enabling neuroplasticity that deters relapse to cocaine self‐administration.The authors declare no competing financial interests. These studies were supported by NSF grant SMA-0835976 to the CELEST Science of Learning Center at Boston University and by NIH grants DA024315 (KMK) and MH079407 (HYM). We thank Iris Mile, Zachary Silber, Sharone Moverman and Enjana Bylykbashi for expert technical assistance. (SMA-0835976 - NSF; DA024315 - NIH; MH079407 - NIH)https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4798903/Published versio