[{"id":20,"title":"The Galactic Astigmatism: Constraining the Milky Way Dark Matter Halo Using Ultra-Weak Lensing","sha":"86fd4606f693acf5f94c2808e69804d1","user_id":14,"state":"published","body":"An astigmatism is defined as an asymmetry of the front of the eye, causing light to not focus on a single point. Because the Sun is located ~8kpc off-center in the Milky Way, the integrated mass density of galactic dark matter varies significantly along different lines of sight. As a result, the Milky Way's own DM halo will act as a gravitational lens, magnifying background sources more along lines of sight toward the bulge, and less towards the anti-center. While such lensing may be very weak, it is decidedly non-zero. This ultra-weak lensing may be detected in the number density or apparent brightness of (for example) distant galaxies.\r\n\r\nI note also, this effect has been mentioned only once in the literature that I am aware of, by [Xu and Wu (1987)](http://adsabs.harvard.edu/abs/1987IAUS..124..771X), who speculate the brightness amplification signal may as large as 1e-6 to 1e-5, and possibly detectable in precision CMB data.","created_at":"2015-02-04T22:08:51.143Z","updated_at":"2018-02-19T06:00:28.098Z","zenodo_id":21481,"doi":"http://dx.doi.org/10.5281/zenodo.14841","subject":null,"tags":["astronomy","galaxies","darkmatter","speculation"],"vote_count":13,"view_count":1,"score":13.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null},{"id":333,"title":"Searching for \"Tabby's Star\" Analogs in Stripe 82","sha":"534f2373fdf0cd3de184f11a63c4a3ee","user_id":null,"state":"published","body":"[\"Tabby's Star\"](http://adsabs.harvard.edu/abs/2016MNRAS.457.3988B) is an anomalous F star with repeated short-term variability, and a steady [3% dimming over 4-years](http://adsabs.harvard.edu/abs/2016arXiv160801316M). The star spent [~8%](https://twitter.com/Nighthawk_Black/status/762410345411469312) of the Kepler 4-year light curve in the short-duration dimming state. As [LaCourse](/ideas/59bde655f99d29f685702717316e06f3) notes, no analog has been found with [Kepler](http://adsabs.harvard.edu/abs/2010Sci...327..977B). Neither the short- or long-term variability in this object are currently understood so discoveries of additional examples are desperately needed. \r\n\r\n[Stripe82](http://adsabs.harvard.edu/abs/2007AJ....134..973I) was a 10-year multi-epoch photometric catalog by [SDSS](http://adsabs.harvard.edu/abs/2000AJ....120.1579Y), covering ~300 sq deg with 70-90 epochs in *ugriz*. More than 10,000 objects were identified as [variable](http://www.astro.washington.edu/users/ivezic/sdss/catalogs/stripe82.html) with [F star colors](http://adsabs.harvard.edu/abs/2007AJ....134.2398C) from Stripe82, with many likely pulsators or eclipsing binaries. The photometric precision of Stripe82 is sufficient to detect the long-term, non-stationary variability observed from \"Tabby's Star\". Additionally, the 8% duty cycle of short-term dimming events should stand out as several aperiodic outliers in the Stripe82 light curves. Finally, the near-simultaneous multi-band data from SDSS may provide important clues as to nature of this new class of variable star.","created_at":"2016-08-15T21:57:38.909Z","updated_at":"2016-09-01T14:11:31.029Z","zenodo_id":145722,"doi":"http://dx.doi.org/10.5281/zenodo.60308","subject":null,"tags":["kepler","astronomy"],"vote_count":4,"view_count":1,"score":4.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null}]