U Sco 2010: 食の観測キャンペーン 1月28日に爆発した回帰新星 U Sco の食がいよいよ見える ような状況になってきています。この食の観測の世界的な キャンペーンをアメリカのシェーファーがCBAで提起して います。日本でも、ぜひ参加しましょう。 食が観測できるとどのようなことが分かるのかを簡単に 解説しておきますと、 (1) 連星の軌道周期が分かりますので、もし、軌道周期に 変化があると、角運動量と質量の変化が分かります。 これから、爆発した白色矮星がどのくらいのガスを失った か、2010年の爆発と1999年爆発の間にどの程度のガスが 移動したか、などが推定できて、白色矮星が太るのか、 それとも、やせるのか、が分かり、U Sco がIa型超新星に なれるかどうか、が分かるかもしれません。これは 天文学的に重要な問題ですので、大きな貢献となります。 (2) 最近の IAUC 9114 (2010年2月5日付)によると、 フリッカーリングと呼ばれる光度曲線の短時間変動 (0.2等で数十分ほどの時間変動)が受かっているようです。 これは、白色矮星への質量降着が起こっている証拠と 言われています。爆発後7日で、伴星からの降着が復活(？) したので、降着円盤が存在していることになります。 主極小や副極小が観測されると、降着円盤の大きさや、 形状などにある程度の制限がつき、爆発中の様子をより 詳しく知るでがかりになります。(明るい白色矮星からの 照り返しで、円盤が光っていると思われています。) (3) y フィルターの観測ができるかたは、ぜひお願いします。 RS Ophの時は、yとV等級はほぼ同じでしたが、同じかそうで ないかは、平坦期にはいったときに重要なります。平坦期が 輝線の寄与によるみかけのものなのか、disk が照り返されて 明るいのかを決める重要なファクターとなります。暗くなって くると大変だと思いますが、よろしくお願いします。 U Sco は、現在、V=11.5等程度まで暗くなっていますが、 1999年の爆発の時は、爆発後35日程度まで、V=14-15等程度の 明るさが持続しました。今回の爆発では、3月中頃までは、 14-15等程度の明るさですので、小口径の望遠鏡でも十分観測 できると思います。明け方の短い時間ですが、日本でも十分 観測できます。ぜひ、チャレンジしてみてください。 観測結果は、vsolj-obs に投げてください。 また、同時に、vsnet-campaign-report@ooruri.kusastro.kyoto-u.ac.jp にも投げてください。 シェファーが、 CBA に流したもの(英文)を最後に付けておきます。 食(主極小)の予報ですので観測の参考にしてください。主極小だけでなく、 その中間の副極小(軌道周期は1.23日)も狙い目です。 蜂巣 ----- U Sco 用のページ http://lyman.c.u-tokyo.ac.jp/~hachisu/novae/u_sco2010/u_sco.html ---------------------------------------------------------------------- Date: Thu, 4 Feb 2010 12:42:36 -0600 (CST) From: Brad Schaefer To: cba-news@cba.phys.columbia.edu Subject: (cba:news) High-science from CBA observations of U Sco Hi; Just about now, the recurrent nova U Sco (now at V=11.5 in its eruption just one week old) will start showing eclipses, and there is high science from getting detailed time series of these eclipses. And the CBA is perfect for getting exactly that. So I am appealing that all hands take long time series of U Sco around these eclipses when U Sco is up in the pre-dawn sky. (Even northern hemisphere observers can get a few hours, and we need this to patch together the whole eclipse light curve.) In quiescence, U Sco has a deep *total* eclipse. This provides a unique and wonderful opportunity to do important front-line science between now and early March, even with smallish-telescopes. Here are three big-time science items that CBA is perfect to get: (1) Eclipse mapping of the light distribution across the photosphere. As the companion star blocks out the optical light from the photosphere around the white dwarf, the variations will define the size and structure of the photosphere. Such has never been done before. (2) The center of the eclipse timings can be used with the center of eclipse timings in the tails of the last two eruptions (1987 and 1999) so as to determine the change in the orbital period across the 1999 eruption. This change will by Kepler's Law translate directly into a mass ejected. This method is the only reliable way to get the ejected mass (the other *old* ways are all horribly assumption ridden and they are accurate only to perhaps 1-2 orders of magnitude). And the knowing the ejected mass will tell us whether the white dwarf is net gaining in mass over each eruption cycle, and this will directly answer the old uber-important Type Ia supernova progenitor problem. (3) The eclipse depth varies from early in the eruption when the expanding shell is optically thick until late in the tail when it is optically thin. A measure of the eclipse depth will directly give the optical depth from the center of the binary all the way out. This will then (for knowing the opacity of the shell from physics) translate into the total mass ejected. This is a totally new way of measuring the mass ejected, and I want to try this on the U Sco eruption. This method is totally independent of the big-troubles of the old methods (like uncertain distances, filling factors, ionization states...), and hopefully will be good. Then, as in item 2, we get the mass ejected and this plays into the uber-important Type Ia SN progenitor problem. So we've got big stakes to play for, and CBA is perfectly set up. First, you have a good distribution in longitude, with this allowing for coverage of mulitple eclipses. Second, you have multiple observers with distribution in longitude, as this is required to patch together light curves to get a whole eclipse. The problem is that U Sco is close enough to the Sun, that any one observer can only cover 1-3 hours between U Sco rise and dawn, so multiple observers are required to cover the ~6 hour duration elcipses. Third, you don't have large scopes, and you are set up perfectly for time series photometry. U Sco is now at V=11.5, and by the end of March it will be V=14. This is just perfect for CBA and useless for the big scopes. So here are the details of what to do. Use the list below to select which mornings will have U Sco observable for your location for times within 5 hours of the quoted eclipse center times. (We must have observations around 5 hours of so on either side of eclipse so as to know the uneclipsed level.) When U Sco rises high enough (push this a little if you can), start taking your normal time series and just keep at this until dawn makes you stop. Choose the shortest reasonable exposure time such that U Sco and one of the comparison stars (preferrably COMP) are not saturated. For the comparison stars, see the attached files (in PDF and WORD formats) for finder charts on all scales as well and the magnitudes for all the indicated stars. If you have a V-filter then use it (R-band is the only other option to use). If you need more signal or do not have a V or R filter, then simply run without any filter. After dawn, process your images (bias subtract, flat field...) in the usual way. Extract the magnitude of U Sco with aperture photometry in comparison with one or more of the stated comparison stars (preferably COMP). Send these magnitudes to the usual CBA data site. It is all easy, and much of what you already do so well. Here is a table with all the eclipse times from now to early March: JD mid-eclipse UTmid UT date Where Visible 2455232.571 1:43 5-Feb South Africa 2455233.802 7:15 6-Feb Florida, Chile 2455235.032 12:47 7-Feb Calif, Hawaii 2455236.263 18:18 8-Feb NZ, Australia 2455237.493 23:50 9-Feb South Africa 2455238.724 5:22 11-Feb Chile 2455239.954 10:54 12-Feb Florida-Calif 2455241.185 16:26 13-Feb Hawaii, NZ, Australia 2455242.416 21:58 14-Feb Aus-SA 2455243.646 3:30 16-Feb South Africa 2455244.877 9:02 17-Feb Florida-Calif 2455246.107 14:34 18-Feb Hawaii, NZ 2455247.338 20:06 19-Feb Aus-SA 2455248.568 1:38 21-Feb South Africa 2455249.799 7:10 22-Feb Florida, Chile 2455251.029 12:42 23-Feb Calif, Hawaii 2455252.260 18:14 24-Feb NZ, Australia 2455253.491 23:46 25-Feb Aus-SA 2455254.721 5:18 27-Feb Chile 2455255.952 10:50 28-Feb Florida-Calif 2455257.182 16:22 1-Mar Hawaii, NZ, Australia 2455258.413 21:54 2-Mar Aus-SA 2455259.643 3:26 4-Mar South Africa 2455260.874 8:58 5-Mar Florida-Calif 2455262.104 14:30 6-Mar Hawaii, NZ 2455263.335 20:02 7-Mar Australia 2455264.565 1:34 9-Mar South Africa 2455265.796 7:06 10-Mar Florida, Chile 2455267.027 12:38 11-Mar Calif, Hawaii The eclipses should be just starting as shallow events now, and after early March then U Sco will likely have a sudden drop in brightness making it hard to get eclipses. This is easy, this is exciting, this is big-time science, and only the CBA can do this! Cheers, Brad schaefer@lsu.edu