82,942 research outputs found

    DIRBE Minus 2MASS: Confirming the Cosmic Infrared Background at 2.2 Microns

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    Stellar fluxes from the 2MASS catalog are used to remove the contribution due to Galactic stars from the intensity measured by DIRBE in four regions in the North and South Galactic polar caps. After subtracting the interplanetary and galactic foregrounds, a consistent residual intensity of 14.8 +/- 4.6 kJy/sr or 20.2 +/- 6.3 nW/m^2/sr at 2.2 microns is found. At 1.25 microns the residuals show more scatter and are a much smaller fraction of the foreground, leading to a weak limit on the CIRB of 12.0 +/- 6.8 kJy/sr or 28.9 +/- 16.3 nW/m^2/sr (1 sigma).Comment: ApJ in press. 14 pages Latex with 7 included figures. accepted version with 1 new figur

    COBE Observations of the Cosmic Infrared Background

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    The Diffuse InfraRed Background Experiment on COBE measured the total infrared signal seen from space at a distance of 1 astronomical unit from the Sun. Using time variations as the Earth orbits the Sun, it is possible to remove most of the foreground signal produced by the interplanetary dust cloud [zodiacal light]. By correlating the DIRBE signal with the column density of atomic hydrogen measured using the 21 cm line, it is possible to remove most of the foreground signal produced by interstellar dust, although one must still be concerned by dust associated with H_2 (molecular gas) and H II (the warm ionized medium). DIRBE was not able to determine the CIRB in the 5-60 micron wavelength range, but did detect both a far infrared background and a near infrared background. The far infrared background has an integrated intensity of about 34 nW/m^2/sr, while the near infrared and optical extragalactic background has about 59 nW/m^2/sr. The Far InfraRed Absolute Spectrophotometer (FIRAS) on COBE has been used to constrain the long wavelength tail of the far infrared background but a wide range of intensities at 850 microns are compatible with the FIRAS data. Thus the fraction of the CIRB produced by SCUBA sources has large uncertainties in both the numerator and the denominator.Comment: Invited paper presented at the 2nd VERITAS Symposium on TeV Astrophysics of Extragalactic Sources, April 24-26, 2003 at the Adler Planetarium in Chicago. 8 pages LaTeX with 3 embedded figure

    Population ageing and immigration policy

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    In its simplest interpretation, population ageing is the increase in the average or median age of a population. It is the process by which there is a redistribution of relative population shares away from the younger to the older age groups

    Preparing Preservice Teachers for the Experimental Design and Data Analysis SOL\u27s

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    Many elementary teachers ïŹnd teaching the science Standards of Learning (SOL) difficult [1, 2]. Some are even threatened by them. Of particular concern are the SOLs related to experimental design, handling data, and the scientific method. A possible reason for this discomfort is because many of these elementary teachers have had limited-to-no exposure to experimentation. As one of the activities included under a recent National Science Foundation Science Teachers Enhancement Project (STEP) grant awarded to Hampton University in conjunction with Virginia Union University and St. Paul\u27s College, we included a teacher science fair competition. A special workbook/text was developed for this project and used to guide teachers through the research process; from observation, and hypothesis formation and testing through the evaluation of data and drawing conclusions from the experiment. Twenty-two teachers from the Richmond metropolitan area and King and Queen County developed individual projects (laboratory research), and prepared written reports and display boards to present their results. Projects were adjudicated by staff at the Science Museum of Virginia in a formal competition for teachers. Several teachers admitted that this was the ïŹrst time that they had actually performed a full experiment. All participants agreed, at. the end, that they had a much better understanding of the process, and would be better able to teach it to their students. This successful activity is being submitted to the review panel as a reproducible model which affords preservice teachers an opportunity to strengthen their research skills. It can also make teachers feel more conïŹdent, and equip them to do a better job of teaching this block of SOLs

    Starting life in Scotland in the new millennium : population replacement and the reproduction of disadvantage

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    Scotland, in line with the rest of Europe, is experiencing low rates of child-bearing and its population is ageing. This does not necessarily mean that people in Scotland are going grey at a faster rate than they used to. Rather, it means that there is an increasing proportion of elderly people in its population, with more people who are growing old than are growing up. The "birth dearth" and "population greying" are not unconnected: low fertility is the key influence on the age structure of a population as well as the rate of population growth

    DIRBE Minus 2MASS: Confirming the CIRB in 40 New Regions at 2.2 and 3.5 Microns

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    With the release of the 2MASS All-Sky Point Source Catalog, stellar fluxes from 2MASS are used to remove the contribution due to Galactic stars from the intensity measured by DIRBE in 40 new regions in the North and South Galactic polar caps. After subtracting the interplanetary and Galactic foregrounds, a consistent residual intensity of 14.69 +/- 4.49 kJy/sr at 2.2 microns is found. Allowing for a constant calibration factor between the DIRBE 3.5 microns and the 2MASS 2.2 microns fluxes, a similar analysis leaves a residual intensity of 15.62 +/- 3.34 kJy/sr at 3.5 microns. The intercepts of the DIRBE minus 2MASS correlation at 1.25 microns show more scatter and are a smaller fraction of the foreground, leading to a still weak limit on the CIRB of 8.88 +/- 6.26 kJy/sr (1 sigma).Comment: 25 pages LaTeX, 10 figures, 5 tables; Version accepted by the ApJ. Includes minor changes to the text including further discussion of zodiacal light issues and the allowance for variable stars in computing uncertainties in the stellar contribution to the DIRBE intensitie