H. G. Marraco

SN 1987A - a linear polarimetric study

Multicolor linear polarimetric observations of SN 1987A have been obtained between February 28 and April 29, 1987. The intrinsic polarization was shown to decrease at a constant position angle of 27 deg during the first month after the explosion, and 30 days after the explosion the polarization began to grown in the V, R, and I filters at a different position angle. A model to interpret this behavior is proposed. Results are presented for the expansion of the outer layers of the SN and the evolution of the photospheric density. 28 references.

AN IMPROVED METHOD TO DERIVE PERIODS OF CYCLIC PHENOMENA

Two simple improvements are presented to Jurkevichs method (1971) for deriving periods of variable stars; the method is particularly useful when large numbers of observations are available. An example (the case of HD 217792) of the results of both the original and improved methods is presented.

Intracluster dust polarization in the Carina Nebula

We have obtained new UBVRI polarimetric observations of 25 stars and BV polarimetric observations of 60 stars which are embedded in the Carina Nebula. Using these data and photometric data from the literature we have modeled and subtracted the foreground dust contribution in the color excess E B−V and the visual polarization. The resulting intracluster dust component is found to have a polarization efficiency less than the maximum observed for the interstellar medium.

THE OPEN CLUSTER NGC 3293 AND THE OB COMPLEX IN CARINA.

Photoelectric measures in UBVRI of 46 stars in and around the open cluster NGC 3293 are presented. A distance modulus of V0 - Mv equals 12.1 plus or minus 0.15 (s.d.), corresponding to 2.6 kpc, was derived from the photometric data for 34 member stars. This is similar to distances found for other young groups in the Carina region. One M supergiant and one Be star are members of the cluster. The brightest stars on the main sequence are of type B1. Several stars that have evolved away from the upper main sequence have been classified as giants and supergiants. The age of the cluster is about 7-million years. The star HD 91824 (no. 1), spectral type O7 V((f)), is not a member of the group. The insterstellar reddening is normal in front of this cluster.

NIRST: a satellite-based IR instrument for fire and sea surface temperature measurement

NIRST is a pushbroom scanning infrared radiometer that makes use of 512×2 arrays of resistive microbolometers. This instrument comprises mainly two cameras, one operating in the spectral band of 3.4-4.2 μm (band 1) and the other in the bands of 10.4-11.3 (band 2) and 11.4-12.3 μm (band 3). It is intended for the retrievals of forest fire and sea surface temperatures in the Aquarius / SAC-D mission. In this mission the satellite will be launched into a Sun Synchronous polar orbit with an ascending node at 6 PM. This orbit suits the need of discriminating forest fires from solar reflections. NIRST is designed to achieve a spatial resolution of 350 m and a swath width of 180 km at nadir. Its field of view can be steered across track up to 500 km on each side to shorten the revisit time. To measure fire intensity temperatures NIRST will perform multispectral scans of ground area in bands 1 and 2 and the acquired data will be analyzed using a double band algorithm. The microbolometer detectors have been designed to exhibit useful dynamic range for this application. It is projected that the detector response in band 1 saturates only when NIRST scans a 350 m ground pixel of average temperature of 700 K. The use of the data acquired in bands 2 and 3 allows for the retrieval of sea surface temperature by means of the split algorithm technique.

Performances of the SAC-D NIRST flight model radiometer

Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space Administration of the United States of America and the Comisión Nacional de Actividades Espaciales of Argentina. Jointly developed by CONAE and the Canadian Space Agency, the New IR Sensor Technology (NIRST) instrument will monitor high temperature events. NIRST has one band in the mid-wave infrared and two bands in the thermal infrared. The baseline design of the NIRST is based on microbolometer technology developed jointly by INO and the CSA. This paper will first present an overview of the design of the NIRST camera module. The manufacturing and qualification activities for the Flight Model will be described and key performance parameters, as measured during the verification campaign, will be reported.

Design of the SAC-D/NIRST camera module

Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space Administration (NASA) of the United States of America (USA) and the Comisión Nacional de Actividades Espaciales (CONAE) of Argentina. The overall mission targets the understanding of the total Earth system and the consequences of the natural and man-made changes in the environment of the planet. Jointly developed by CONAE and the Canadian Space Agency (CSA), the New IR Sensor Technology (NIRST) instrument will monitor high temperature events on the ground related to fires and volcanic events, and will measure their physical parameters. Furthermore, NIRST will take measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities. NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um. The temperature range is from 300 to 600 K with an NEDT < 0.5 K for the mid-infrared band and from 200 to 400 K with an NEDT < 0.4 K for the thermal bands. The baseline design of the NIRST is based on micro-bolometer technology developed jointly by INO and the CSA. Two arrays of 512x3 uncooled bolometric sensors will be used to measure brightness temperatures. The instantaneous field-of-view is 534 microradians corresponding to a ground sampling distance of 350 m at the subsatellite point. A pointing mirror allows a total swath of +/− 500 km. This paper describes the detailed design of the NIRST camera module. Key performance parameters are also presented.

NEAR INFRARED EXCESSES IN BE STARS.

Sixty-eight bright Be stars were observed in the R and I bands of the Johnson system. Nearly all of them lie above the main sequence in a (B - V,V- I) diagram, which is interpreted as a near-infrared excess (ΔI) in their energy distributions. From the computed difference with the standard main-sequence relation, a correlation of this ΔI value with the emission strength of the Hα line, previously defined as eα is found. On the other hand, the ultraviolet excesses derived from the Q values shows no evidence of correlation with the infrared excesses. But a correlation with polarimetric data appears reliable.

Polarimetry in the Outskirts of NGC 6611

We present new polarimetric UBVRI observations of 25 stars in the direction of the halo of NGC 6611, the rich stellar open cluster embedded in an ionized hydrogen complex (M16). Our plan is to characterize the interstellar material (ISM) associated with halo stars in order to make a comparison with the ISM dusty core characteristics that resulted from a previous investigation by the same authors. Of the halo stars, 47% (8 out of 17) show indications of intrinsic polarization in their light, similar to what was found for core stars (50%). We have identified the presence of nearby dust clouds located on the Local arm that produce a mean polarization of about 1%; a value = 0.61 ± 0.07 μm, which is slightly larger than that of the average ISM; and a mean direction of the polarization vectors of = 819 ± 18. The ISM associated with the halo region has similar to the general interstellar medium (0.55 ± 0.07 μm). The observed polarizations show a gradual increase from halo ( = 1.93% ± 0.3%) to core ( = 3.19% ± 0.63%). Position angles of the e-vector for both groups are generally similar, but there exists a slight difference in mean direction between them that is within the errors. We have also found that the halo stars are possibly represented by Whittet & van Bredas relationship, while in the clusters core the dust does not fulfill the above-mentioned relationship. As a conclusion, we cannot find any clear difference between core and halo dust characteristics, with the exception of , which may suggest a change in dust size.

Pismis 20: One or two clusters?

We present UBVRI polarimetric observations of stars in the direction of the open cluster Pismis 20 and WR 67. It is found that the observed members segregate polarimetrically into two groups, with different associated mean