IR emission and UV extinction in two open clusters

Recent models of interstellar extinction have shown the importance of understanding both the UV and IR properties of interstellar dust grains. IRAS data have shown variations in 60 and 100 micron emissions presumably due to the presence of IR cirrus, while recent observations in the UV by Fitzpatrick and Massa have identified components in the UV extinction curve which vary in different star regions. A Draine and Anderson model connects these results by proposing that different size variations in interstellar grains would cause distinct changes in both the IR emission and the UV extinction. In order to test this model it is necessary to make observations in well defined locations away from peculiar extinction regions. In the infrared this means looking away from the galactic plane so as to limit non-local sources of IR radiation. Two open clusters that are out of the galactic plane and which contain a number of late B and early A stars suitable for UV extinction studies, and whose IRAS data show variations in the 60/100 micron ratio were studied. Based on the Drain and Anderson model, variations were expected in their UV extinction curves that correlate with the IR cirrus emission

H and K maps of two star-forming regions: S 140 and CEP A OB3

The molecular clouds near S 140 and Cep A OB3 both contain regions that emit strongly in the infrared but which have relatively little or no emission in radio wavelengths. The lack of radio emission is usually interpreted to mean that little ionization has taken place, and that the IR emission comes from dust heated by a central pre-main sequence object. We have made high resolution maps of these two areas with H and K broadband filters with the 2.3m telescope of the Wyoming Infrared Observatory (WIRO). Our observations were made with an InSb detector using the standard WIRO mapping technique of multiple scanning to construct a series of 64x64 pictures. Our scanning was made in one arcsec steps with a 7 inch aperture to produce a resolution of about 6 sec FWHM. Observations of S 140 by Blair et al (1978) with moderate resolution in J, H, and K, revealed a prominent IR source that they called S 140IR. We have scanned an area surrounding their S 140IR region and have obtained total IR fluxes which are in close agreement with Blair et al. Additional detail corresponds to that seen by Dinerstein et al (1979) at 0.9 microns and Campbell (1986) at 1.0 microns. The large (H-K) values for all components of S 140IR indicates that they are probably embedded in the parent molecular cloud with A(v) = 25 mag and A(K) = 2.2 mag. Recent radio studies of Cep A by Hughes and Wouterloot (1984) and FIR studies by Evans et al (1981) have shown the similarity of Cep A to S 140. There is, however, some emission detected from ionized regions by the radio observations, indicating a slightly more advanced stage of evolution for Cep A. We observed an area around the strongest source in Cep A in both H and K, and the K map is presented. We have identified three sources separate from the main source

Observational constraints on interstellar dust models

No single model has been able to account for all of the observed spectroscopic properties of interstellar or circumstellar dust. The reason for this is that, despite the agreement that the grains are composed of silicaceous/metal oxide and carbonaceous material, there is strong disagreement as to their exact structure and composition. This led Draine and Lee (1984) to use interstellar extinction data to define an interstellar graphitic material; new observational findings have made even that identification uncertain. But the great advantage of their approach is that they used observations at all of the wavelengths available to define the material. Here, the authors attempt a variation of that approach. They examine recent UV and IR data and attempt to put constraints on the possible types of interstellar grain composition, and to connect these constraints with grain models. A summary of some of the important constraints imposed by the observations is given

The Link Between UV Extinction and Infrared Cirrus

Low resolution spectra from the International Ultraviolet Explorer satellite were used to derive ultraviolet extinction curves for stars in four clusters away from the galactic plane. The extinction in three of the clusters is very similar to the general interstellar curve defined by Seaton. Stars in the fourth region, near the Rho Ophiuci dark cloud, have extinction curves that are characterized by a small "linear" term component. The star BD +36 deg 781 is unique amongst the 20 stars observed in that it shows evidence for extinction by diamond grains near 1700 angstroms. We used data from the final release of the IRAS Sky Survey Atlas (ISSA) to determine the 60 micron to 100 micron intensity ratio for the infrared cirrus. The ISSA data, which have been corrected for zodiacal light, gave intensity ratios that are more robust and self-consistent than for other data sets that we used. When the infrared and ultraviolet data are combined, we see a general trend for low values of the ultraviolet "linear term" (al) to correlate with high values of 60 micron/100 micron ratio. This implies that, in regions where the average dust temperature is hotter (high 60 micron/100 micron ratio), there is a relative absence of the small silicate grains that are responsible for the ultraviolet linear term. However, the new data do not bear out our earlier contention that the 60 micron and 100 micron emissions are poorly correlated spatially in regions where the 60 micron/100 micron ratio is low. Only NGC 1647 shows this result. It may be that the different dust types are particularly poorly mixed in this area

Quantifying Bar Strength: Morphology Meets Methodology

A set of objective bar-classification methods have been applied to the Ohio State Bright Spiral Galaxy Survey (Eskridge et al. 2002). Bivariate comparisons between methods show that all methods agree in a statistical sense. Thus the distribution of bar strengths in a sample of galaxies can be robustly determined. There are very substantial outliers in all bivariate comparisons. Examination of the outliers reveals that the scatter in the bivariate comparisons correlates with galaxy morphology. Thus multiple measures of bar strength provide a means of studying the range of physical properties of galaxy bars in an objective statistical sense.Comment: LaTeX with Kluwer style file, 5 pages with 3 embedded figures. edited by Block, D.L., Freeman, K.C., Puerari, I., & Groess,

The biology and behavior of the alkali bee Nomia melanderi Cockerell (Hymnoptera:Apoidea)

Nomia melanderi Cockerell is one of the most efficient pollinators of alfalfa in Eastern Oregon. Emergence begins in June, usually reaches its peak in early July, and may continue into early August. Male emergence precedes female emergence by four or five days. For the first few weeks of this time, the males spend the morning hours patrolling the nesting area. As each new female bee emerges, many males attempt to mate with her , but most contacts are unsuccessful. Soil temperature and moisture are the prime factors influencing emergence. After mating has been accomplished, the female bee forages in the field and returns to the bee bed in the afternoon to begin nest construction. The male also spends the afternoon in the field, returning to spend the night in clusters on plants on, or in the vicinity of the bee bed. Some crawl under the loose soil crust, paper, sticks, rocks, or enter burrows for the night. The female, after digging herself under the soil surface, spends the nest two or three days roughing out cells. On the third, fourth or fifth day she begins to collect pollen. She usually forages on blossoms close to the nest, tripping about 96 percent of those visited. The female gradually increases her foraging range, moving progressively further from the nest as she ages. The time required to complete each pollen collecting trip varies considerably, but averages close to 35 minutes. It takes from seven to 11 trips to complete one pollen ball and this may require from 5 1/2 to 9 hours. The female trips the alfalfa blossom by forcing its head against the standard petal while its legs are braced against the wing petals. Mortality is evidenced by an abrupt decline in the number of working females. Eggs of Nomia melanderi require from 2 1/2 to 3 days to hatch. The larva passes through five instars. The fifth instar defecates after all the pollen has been consumed, and transforms into the prepupa, which passes through the winter. The following spring the prepupa transforms into the pupa which shortly develops into the mature adult. The alkali bee uses major and minor landmarks for orientation. Larger landmarks such as haystacks, trees, fences, roads , and ditches are used to locate the bee bed. Then smaller markers such as soil clods, sticks, etc. are used to locate the individual burrow opening. Preliminary studies suggest that the alkali bee is able to distinguish among yellow, green, blue, white and gray colors. Temperature is usually the limiting factor in the initiation of morning activity, whereas light intensity appears to determine the time of flight cessation in the evening

High spatial-resolution IRAS images of M51

High spatial-resolution (approx. equal to 30 seconds) images of M51 in the four Infrared Astronomy Satellite (IRAS) bands (12, 25, 60, and 100 microns) have been obtained. The spatial variation in flux in all four bands is coincident with the spiral features seen in H alpha and 6 cm with a few exceptions. In the nuclear region (4 minutes) the position of the peak of maximum intensity shifts in relation to the visual nucleus: it is coincident with the nucleus at 12 microns, shifts approximately 45 seconds to south-southwest, and is 45 seconds northwest of the nucleus at 60 and 100 microns

A correlation between infrared excess and period for Mira variables

The [8.7]-[11.4] infrared color is found to increase monotonically with increasing period for a sample of 41 Mira variables. We conclude that mass loss is not a stochastic process and that for any Mira variable the rate of mass loss is directly linked to the parameters which dictate the period of that variable

Mid-infrared spectra of late-type stars: Long-term evolution

Recent ground-based mid-infrared spectra of 29 late-type stars, most with substantial dust shells, are compared to ground-based spectra of these stars from the 1960s and 1970s and to IRAS-LRS spectra obtained in 1983. The spectra of about half the stars show no detectable changes, implying that their distributions of circumstellar material and associated dust grain properties have changed little over this time interval. However, many of the stars with strong silicate features showed marked changes. In nearly all cases the silicate peak has strengthened with respect to the underlying continuum, although there is one case (VY~CMa) in which the silicate feature has almost completely disappeared. This suggests that, in general, an oxygen-rich star experiences long periods of gradual silicate feature strengthening, punctuated by relatively rare periods when the feature weakens. We discuss various mechanisms for producing the changes, favoring the slow evolution of the intrinsic dust properties (i.e., the chemical composition or grain structure). Although most IRAS spectra agree well with ground-based spectra, there are a number of cases where they fall well outside the expected range of uncertainty. In almost all such cases the slopes of the red and blue LRS spectra do not match in their region of overlap.Comment: Accepted in ApJ, 20 pages, 5 figures, 1 tabl

Episodic Post-Shock Dust Formation in the Colliding Winds of Eta Carinae

Eta Carinae shows broad peaks in near-infrared (IR) JHKL photometry, roughly correlated with times of periastron passage in the eccentric binary system. After correcting for secular changes attributed to reduced extinction from the thinning Homunculus Nebula, these peaks have IR spectral energy distributions (SEDs) consistent with emission from hot dust at 1400-1700 K. The excess SEDs are clearly inconsistent, however, with the excess being entirely due to free-free wind or photospheric emission. One must conclude, therefore, that the broad near-IR peaks associated with Eta Carinae's 5.5 yr variability are due to thermal emission from hot dust. I propose that this transient hot dust results from episodic formation of grains within compressed post-shock zones of the colliding winds, analogous to the episodic dust formation in Wolf-Rayet binary systems like WR140 or the post-shock dust formation seen in some supernovae like SN2006jc. This dust formation in Eta Carinae seems to occur preferentially near and after periastron passage; near-IR excess emission then fades as the new dust disperses and cools. With the high grain temperatures and Eta Car's C-poor abundances, the grains are probably composed of corundum or similar species that condense at high temperatures, rather than silicates or graphite. Episodic dust formation in Eta Car's colliding winds significantly impacts our understanding of the system, and several observable consequences are discussed.Comment: MNRAS accepted; 8 pages, 5 figs, 2 color fig