BAAS 37, 490 2005 UV ISM Polarization of Galactic Starlight II. More Observations by WUPPE (Wisconsin Ultraviolet Photo-Polarimeter) A.J. Weitenbeck, C.M. Anderson, A.D. Code, K.S. Bjorkman, M.R.Meade, B.L. Babler, J.J.Johnson, G.K. Fox, N.E.B.Zellner University of Wisconsin Space Astronomy Lab ABSTRACT Besides the stars with ISM polarization given in Anderson et al. (AJ 112, 2726) WUPPE obtained observations of several other stars which were targets of or were in the fields of targets of the other instruments on the ASTRO-2 Mission. For northern targets HD51285, HD31726, NGC2682 81 and BD+36 367 we will show observations made with WUPPE and HPOL (UW spectropolarimeter); for southern stars HD177999 and HD68049, we show only WUPPE data. These data are consistent with the general findings of Anderson et al. that the ISM polarization continues to decrease into the UV. WUPPE was supported by NASA contract 5-26777. www.sal.wisc.edu/~ajw/wupism2/postrMPL.txt BACKGROUND Anderson et al. (AJ 112, 2726) give WUPPE (Wisconsin UV Photopolarimeter) and ground based polarimetry (mostly with the UW spectropolarimeter, HPOL) of some 30 relatively bright stars mostly selected to be observed as a program to measure ISM polarization in the UV. MORE DATA WUPPE also obtained observations of several other stars with ISM polarization. These were mostly targets of the other instruments on the ASTRO-2 Mission or were stars to which WUPPE offset in the fields of other instruments' targets. Not having been selected specifically for the ISM polarization program, these stars are not necessarily highly polarized or very bright, and, being on other instruments' programs, the observations were not always long enough to obtain high quality polarimetry. Several of these stars have now been observed with HPOL at UW's Pine Bluff Observatory (i.e., they were bright enough and not too far south): HD51285, HD31726, and NGC2682-81. Two others are too far south to observe from Pine Bluff: HD177999 and HD68049, so we give only WUPPE polarimetry for these. Those for which both WUPPE and visible data exist are consistent with the general earlier findings in Anderson et al. (1996) that the ISM polarization decreases from the visible into the UV, though the polarizations of these stars are generally too low to attempt to fit reliable Serkowski curves to the data in order to try to find deviations from the visible curve into the UV. HD177999 is the only clear exception to this, but it needs high quality visible light spectropolarimetry from the Southern hemisphere. BD+36 367 is also shown as an example of a target for which WUPPE made a polarimetric detection, but the uncertainty is large compared to the the polarization, so no definite conclusions can be drawn from the UV data. There are about a dozen other WUPPE observations similar to this (either faint or large uncertainty compared to the polarization); BD+36 367 is the only one observable from PBO. HPOL DATA The whole wavelength range is observed in in two steps, about 3000-6000\AA, and 6000-10500\AA. The polarization is given in the Stoke's parameters Q and U and in per cent polarization and position angle; it is quoted in simulated filter bands computed with the "PFIL" routine giving a flux weighted polarization using simulated filters from the normalized Johnson-Cousins passbands tabulated by Bessell, PASP 102, 1181 (1990). QUOTED ERRORS The quoted HPOL and WUPPE error is an internal uncertainty: HPOL instrumental calibration stability of order .01-.02% in the V band must be added when comparing observations on different nights or with other observers; WUPPE calibration uncertainty is somewhat larger. Q, U, and Error are given with the number of significant figures provided by the software program, since this allows estimation of the relative quality of the observation, but the quoted p is rounded to .01% and postion angle to .1o. PLOTS In figures showing polarization vs. wavelength the data is binned by error (the plot routine starts at short wavelength and adds data until the desired error is achieved, then starts a new bin), or by wavelength (the polarization and its error for that wavelength interval is displayed). Acknowledgements WUPPE was supported by NASA contract 5-26777. This research used the SIMBAD database, operated at CDS, Strasbourg, France. HD31726: A slightly reddened B2V in Orion. A fairly high quality WUPPE observation, but polarization is too low to try to fit Serkowski curve with these HPOL data. Plot: www.sal.wisc.edu/~ajw/wupism2/hd31726.WPHP.ps Wavelengths Q(%) U(%) Error(%) Pol(%) PA WUPPE 1599-1800 -0.0763 0.0178 0.0330 0.08 83.4 1800-2000 0.0910 0.1559 0.0256 0.18 29.9 2000-2200 0.1562 0.1506 0.0248 0.22 22.0 2200-2400 0.0807 0.2124 0.0270 0.23 34.6 2400-2597 0.1470 0.2105 0.0315 0.26 27.5 HPOL U 0.2205 0.0819 0.0305 0.24 10.2 B 0.1928 0.1166 0.0054 0.23 15.6 V 0.1803 0.1489 0.0033 0.24 19.8 R 0.1753 0.1411 0.0021 0.23 19.5 I 0.1434 0.1242 0.0023 0.19 20.4 HD51285: A B2V with H? emission. The polarization is fairly low, and at dec -24 is also too far south to get highest quality HPOL data. The WUPPE and HPOL data are consistent with small ISM polarization. Plot: www.sal.wisc.edu/~ajw/wupism2/hd51285.HPWP.ps Wavelengths Q(%) U(%) Error(%) Pol(%) PA WUPPE 1500-1799 0.0714 0.0772 0.0368 0.11 23.6 1800-2099 0.0459 -0.0078 0.0220 0.05 175.2 2100-2399 0.0252 0.0657 0.0247 0.07 34.6 2400-2699 -0.0014 -0.1149 0.0253 0.11 134.7 2700-2999 -0.0282 -0.0121 0.0364 0.03 101.6 3000-3300 -0.1422 0.1132 0.0841 0.18 70.7 HPOL B -0.2480 -0.1641 0.0198 0.30 106.7 V -0.2534 -0.1780 0.0076 0.31 107.5 R -0.1919 -0.1417 0.0057 0.24 108.2 I -0.1796 -0.1941 0.0069 0.27 113.6 NGC 2682 81: A blue straggler, B8V, in M67. The WUPPE and HPOL blue grating data are each given as one bin. This star is too faint to get high quality HPOL data, but the polarization generally follows a Serkowski curve. The HPOL data are similar to NGC 2682 108, the brightest star in the cluster (Acta Astr 54, 87 2004). Plot: www.sal.wisc.edu/~ajw/wupism2/f81.p.HPWP.ps WUPPE Wavelengths % Q % U % Err % Pol PA 1599 - 3197 -0.0829 0.1359 0.0471 0.16 60.7 HPOL Wavelengths % Q % U % Err % Pol PA 3197 - 6103 0.3089 0.0697 0.0426 0.32 6.4 Filter V 0.2379 0.1363 0.0305 0.27 14.9 R 0.0539 0.1350 0.0162 0.15 34.1 I -0.0744 0.1430 0.0145 0.16 58.7 BD+36 367: A blue straggler, A0III, in NGC 752. The HPOL data is good quality polarimetry when expressed as broad band data, but the WUPPE observation is more of an upper limit. [The V data appears in Acta Astr 54, 87 2004.] Plot: www.sal.wisc.edu/~ajw/wupism2/bd36d367.WPHP.ps WUPPE Wavelengths % Q % U % Err % Pol PA 1599 - 2097 0.7927 0.4699 0.2981 0.92 15.3 HPOL Filter B 0.0427 -0.2480 0.0422 0.26 139.9 V -0.2874 -0.3964 0.0180 0.49 117.0 R -0.3537 -0.3615 0.0252 0.51 112.8 I -0.0290 -0.2765 0.0176 0.28 132.0 HD177999: B9II/III in the field of globular cluster NGC6752; several pointings were made to this cluster, so the WUPPE observation was long enough to be good quality. The WUPPE data are given in 6 equal size wavelength bins over the observed wavelength range. Lupie & Stockman in Polarized Radiation of Circumstellar Origin say the average cluster polarization is .8% at B, .7% in V, at 178 degrees, consistent with the WUPPE data. This star needs high quality spectropolarimetry from the south (dec -60). Plot: www.sal.wisc.edu/~ajw/wupism2/hd177999.WP6bin.ps Wavelengths Q(%) U(%) Error(%) Pol(%) PA WUPPE 1500-1861 wp6bin1 -0.2313 -0.1190 0.0508 0.26 103.6 1862-2127 wp6bin2 0.2444 0.1045 0.0362 0.27 11.6 2128-2393 wp6bin3 0.0391 0.3338 0.0391 0.33 8.4 2394-2657 wp6bin4 0.4115 0.1912 0.0438 0.45 12.5 2658-2922 wp6bin5 0.5319 -0.1592 0.0548 0.56 171.7 2923-3193 wp6bin6 0.4551 0.0085 0.0831 0.46 0.5 HD68049: This star is relatively faint, and the WUPPE exposure was too short to get high quality data, though it appears that the longer wavelength bin shows polarization. Dec = -36, needs visible light spectropolarimetry. Bhatt (MNRAS 308, 40 1999) gives polarization (broad band, unfiltered) .34 +/- .06% at 94 +/- 5 deg. Wavelengths % Q % U % Err % Pol PA WUPPE 1599-2373 -0.0233 0.2471 0.1295 0.25 47.7 2241-3197 0.0159 -0.5865 0.1520 0.59 135.8