[{"id":73,"title":"Extragalactic radio sources as lighthouses for SETI","sha":"be48a68df1c2b616f413017a9138c386","user_id":62,"state":"published","body":"The search for extraterrestrial intelligence (SETI) is one of the most ambitious scientific endeavors. It aims at detecting signals produced intentionally or unintentionally by extraterrestrial civilizations ([Siemion et al., 2013](http://arxiv.org/abs/1412.4867)). The Galaxy, however, is vast and finding suitable telescope targets for SETI is a critical task ([Turnbull \u0026 Tarter, 2003](http://iopscience.iop.org/0067-0049/145/1/181)).\r\n\r\nWe examine a strategy for selecting target areas for (active and passive) SETI aimed at improving chances for success.  The aim is to search for and/or send electromagnetic signals towards and/or from notable extragalactic radio sources.  Assuming that astronomy-wise civilizations are also involved in frequent multi-wavelength monitoring of conspicuous radio sources, the probability for interstellar observers to detect each other when observing in the same direction is increased. A similar idea was proposed by [Lemarchand (1995)](http://link.springer.com/article/10.1007/BF00982337) using Supernova 1987A.  However, radio sources are constant \"lighthouses\" and exist all across the sky.\r\n\r\nFor illustration purposes, we calculate that a signal emitted in a ~1 degree beam in the opposite direction of Centaurus A, could reach ~200 stars, mostly M-dwarfs, at distances \u003c600pc (stellar density model by [Gould et al., 1996](http://iopscience.iop.org/0004-637X/482/2/913)). Conversely if we search for ETI signals around Centaurus A, using the Allen-array (PFOV ~3 degrees, [Deboer et al., 2006](http://link.springer.com/article/10.1007/s10686-005-4193-3)), ~200 stars at distances \u003c300pc will be included in the field and the chance of detecting a message from a civilization using this strategy, is large.","created_at":"2015-02-20T00:46:47.737Z","updated_at":"2018-02-18T07:02:57.524Z","zenodo_id":23173,"doi":"http://dx.doi.org/10.5281/zenodo.15539","subject":null,"tags":["seti","astronomy","astrobiology"],"vote_count":8,"view_count":1,"score":8.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null},{"id":343,"title":"Searching for Dyson spheres with Gaia","sha":"d38a2659d0ba5e167e0428485daf90c8","user_id":null,"state":"published","body":"Assuming that Dyson spheres obscure optical/near-infrared light as grey absorbers, a partial Dyson sphere with high covering fraction (fcov \u003e 0.5) could reveal itself as an anomalously subluminous star with a parallax-based distance smaller than the spectroscopically inferred one. A large catalog search for objects of this type can currently be carried out by combining parallax distances from [Gaia DR1](https://arxiv.org/abs/1609.04303) with spectroscopic distances from [RAVE DR5](https://arxiv.org/abs/1609.03210). From the best-fitting stellar parameters provided by RAVE, the [PARSEC](http://stev.oapd.inaf.it/cgi-bin/cmd) isochrones on which the RAVE fits are based also provide the predicted [WISE](http://wise2.ipac.caltech.edu/docs/release/allsky/) fluxes for these stars. A comparison to the observed WISE flux may then reveal any infrared excess associated with waste heat emission from the Dyson sphere at wavelengths \u003c 22 micron. Most of the ~200,000 stars which are common to both data sets have distance errors too large to be useful for this analysis, but searches among subsets of objects with the highest-quality data and fits could be fruitful. Further cuts can be made to exclude objects which are very young (potentially obscured by debris disks), have left the main sequence (potentially subject to circumstellar dust), or for which the stellar parameters favoured by the RAVE and [RAVE-on](https://arxiv.org/abs/1609.02914) analyses are inconsistent.","created_at":"2016-10-26T06:35:18.744Z","updated_at":"2016-10-29T06:00:25.138Z","zenodo_id":163758,"doi":"https://doi.org/10.5281/zenodo.163758","subject":null,"tags":["seti","gaia","dyson sphere"],"vote_count":0,"view_count":1,"score":0.1,"deleted":false,"muted":false,"tweeted":false,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null}]