PoS(EVN 2014)106 http://pos.sissa.it/ ´ nski, Krzysztof Krzysztof Go´zdziewski, ´ nski [email protected] AM Herculis is a prototypewhite of dwarf the magnetic class field of is magnetic strongthe cataclysmic enough binary variables to called synchronize in "polars". the these rotationaccretion The close of flow binaries. the white is In dwarf directed such with estimation onto a of case the the only magnetic distance accretion pole to streamthese (or polars is very interesting is present poles) stellar crucial systems. and of Here in the we the better presentwith white results understanding the of e-EVN dwarf. of our at astrometric physical project 5 conducted GHz. parameters The of precise Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

12th European VLBI Network Symposium and7-10 Users October Meeting, 2014 Cagliari, Italy Grzegorz Rycyk, Marcin P. Gawro The annual parallax of cataclysmic binaryAM system Herculis with the e-EVN Katarzy Centre for Astronomy, Faculty of Physics, AstronomyUniversity, and Grudziadzka Informatics, 5, Nicolaus 87-100 Copernicus Toru´n,Poland E-mail: PoS(EVN 2014)106 ] 6 ]. [ 9 18 pc was ± 96 88 43 63 43 37 36 31 71 Jy) ± ± ± ± ± ± ± ± 5GHz µ = S d ]. In the other cases, 7 Dec ∆ ]). 1 mJy was reported for polars ] using optical has 1 8 ∼ ]. AM Her was observed to exhibit 3 – VLA archival observations at 8.4 GHz ∗ ] as well as a single 100% circulary polarized 3 ]). 4 pc and recently [ 2 18 15 RA Dec (J2000) + − ∆ (mas) (mas) ( 91 = d 0.3 – 0.7 mJy [ ∼ 18 14 58.5573518 16 13.23569 67 35 49 50 56.1261 49 52 04.9571 41 48 549 597 ∗ ∗ ]), both at C–band. The quiescent emission appears to be nearly always present pc. 4 0.2 – 0.7 mJy. The magnetic field strength was derived 14.5 MG for the primary Date RA (J2000) 7 ]. In 1981 the M4V secondary was detected and the distance ∼ + 6 2 06.02.2013 1802.05.2013 16 13.19321 1817.09.2013 16 13.19224 0.2 1817.09.2013 16 13.18830 0.3 49 52 18 05.119303.12.2013 16 13.18834 0.4 49 52 18 05.1300 0.2 16 13.18806 0.2 49 52 05.1453 0.3 438 0.3 49 52 05.1464 0.4 390 49 52 05.1408 0.2 172 0.2 394 285 05.12.2012 18 16 13.19282 0.2 49 52 05.1122 0.3 290 10.01.1998 17.10.2003 78 Estimated positions and fluxes of AM Her during our astrometric survey. Errors in the position are = d Cataclysmic variables (CVs) are very interesting short-period, close binaries consisting of a The distance estimation of MCVs is fundamental for the interpretation of existing observations AM Her is a prototype of polars and the first discovered member of the class. This flare (9.7 mJy, [ using the K–band methodgiven estimated Table 1: errors from fitting and do not include any systematic effects. in the range usually so–called K–band surface–brightness method is used (e.g. [ non–thermal emission in the range component [ estimated assuming a radius typical of a main sequence for the secondary component [ primary component andcomponent. a low-mass The main-sequence white star dwarf (red accretes(L1) dwarf) material to as from form the the an secondary red accretion dwarfboth. disc, via or the a Magnetic inner magnetically CVs Lagrangian channeled (MCVs)very point accretion are strong stream, defined or magnetic a to fields. combination be Inaccretion of those this onto CVs case the which the magnetic include magnetic poleto field white (or synchronize is dwarfs the poles) strong rotation with of enough of the the to theAM white white direct Herculis dwarf. dwarf the type with flow If binary the of magnetic orbital oroptical-IR period, field polarization "polar". then also is the In is usually system such capable observed isdocumented from a called in the an case the object. only literature. accretion Radio Variable stream detections radio of is emission some present at MCVs and level are of strong and physical models. However, the directoptical measurements of astrometry the were trigonometric done parallax only based for on a the few closest CVs and MCVs so far [ system was also the first to be deteced as a radio source [ Parallax of AM Her 1. Introduction AM Her, V834 Cen, AR UMa and ST LMi (e.g. [ PoS(EVN 2014)106 ± 30 . and the 11 1 . This new = 2 π 0 8 pc ( . 2 observations

model observations ±

5 EVN . − fitted e VLA 88 = −500 d . We also added positions from 1 mas). We conducted calculations using 73 72 . . 0 0 − + −1000 ] 82 . mas [

3 −1680 α 28 ∆ = Dec −1500 µ −1710 mas and 37 35 . . −2000 1 1 − + −1740 ]. Our new astrometric model of AM Her is presented in Fig. package. Maps of the phase calibrator J1818+5017 were created and used 5 44 1 . 71 − = −2500 −1770 780 820 800 RA µ 0 The comparison of our astrometric measurements with the model of the annual parallax and proper 200 600 800 400

−200 −400

] mas [ δ ∆ We are grateful to Polish National Science Centre for their supporthttp://www.aips.nrao.edu/index.shtml (grant no. 2011/01/D/ST9/00735). In order to make a new, more precise distance estimation we conduced a new astrometric 1 35 mas, . Acknowledgement two archival VLA observationsobservations at and made 8.6 GHz more precise to estimationof our of AM AM sample Her Her proper in motion. fitted order The to to astrometric our model expand data the gives time a span new of distanceposterior estimation probability distributions of the fittedestimation astrometric of parameters the is distance shown in tothe Fig. AM literature. Her put this object in the upper limit of the known values from as a model for finalimages. fringe–fitting. The We IMAGR were task ableestimated was to AM used detect to Her produce AM fluxes the Her and final in positions total all intensity are epochs presented of in observations. Tab. Our observations with survey with the e–EVN atduring 5 12 GHz. months Multi– and phase–referencing startedstandard NRAO observations in AIPS were December performed 2012. The data reduction process was carried using Figure 1: motion. The figures shows position offsets of AM Her relative to the first epoch2. of observations. Observations and results the EMCEE package [ Parallax of AM Her 0 PoS(EVN 2014)106 PASP (2003) (1995) , 247 (1982) 107 126 303 ApJ , AJ 225 , A&A , ApJ , ]). The correlation between 5 emcee: The MCMC Hammer (1981) 31 197 The white dwarf in AM Herculis MNRAS Cyclotron features in the infrared spectrum of AM , 4 Radio emission from AM Herculis – the quiescent Parallax and distance estimates for twelve cataclysmic (1983) 249 273 Radio emission from AM Herculis-type binaries A quest for the red companion in six cataclysmic binaries ApJ , measurements uncertainties (EMCEE package, [ (1991) 37 (2008) 2107 σ is caused by large errors from VLA observations. 0 251 136 Parallaxes and distance estimates for 14 cataclysmic variable AJ – Dec , Dec the distances of cataclysmic variables MNRAS µ , and The corner plot presents two-dimensional projections of the posterior probability distributions of (2013) 306 0 3017 variable stars 127 (1981) 960 Herculis component and an outburst 125 – RA RA [8] J.R Thorstensen, S. Lépine and M. Shara, [7] J.R. Thorstensen, [9] P. Young and D.P. Schneider, [2] J. Bailey, L. Ferrario and D.T. Wickramasinghe, [4] G.A. Dulk, T.S. Bastian and G. Chanmugam, [3] G. Chanmugam and G.A. Dulk, [6] B.T. Gänsicke, K. Beuermann and D. de Martino, [1] J. Bailey, [5] D. Foreman-Mackey, D., D.W. Hogg, D. Lang and J. Goodman, µ Figure 2: the fitted parameters with 3 The EVN is a joint facilitytutes of funded by European, their Chinese, national South research African, councils. and other radio astronomy insti- References Parallax of AM Her