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A radial velocity study of the intermediate polar EX Hydrae

A radial velocity study of the intermediate polar EX Hydrae
A radial velocity study of the intermediate polar EX Hydrae
A study on the intermediate polar EX Hya is presented, based on simultaneous photometry and high dispersion spectroscopic observations, during four consecutive nights. The strong photometric modulation related to with the 67-min spin period of the primary star is clearly present, as well as the narrow eclipses associated to the orbital modulation. Since our eclipse timings have been obtained almost 91,000 cycles since the last reported observations, we present new linear ephemeris, although we can- not rule out a sinusoidal variation suggested by previous authors. The system shows double-peaked H?, H? and Hei ?5876 AA emission lines, with almost no other lines present. As H? is the only line with enough S/N ratio in our observations, we have concentrated our efforts in its study, in order to obtain a reliable radial velocity semi– amplitude. From the profile of this line, we find two important components; one with a steep rise and velocities not larger than ?1000 km s?1 and another broader component extending up to ?2000 km s?1, which we interpret as coming mainly from the inner disc. A strong and variable hotspot is found and a stream-like structure is seen at times. We show that the best solution correspond to K1 = 58 ± 5 km s?1 from H?, from the two emission components, which are both in phase with the orbital modulation. We remark on a peculiar effect in the radial velocity curve around phase zero, which could be interpreted as a Rositter-MacLaughlin-like effect, which has been taken into account before deriving K1. This value is compatible with the values found in high- resolution both in the ultraviolet and X-ray. Using the published inclination angle of i = 78 ± 1? and semi-amplitude K2 = 432 ± 5kms?1, we find: M1 = 0.78 ± 0.03 M?, M2 = 0.10 ± 0.02 M? and a = 0.67 ± 0.01 R?. Doppler Tomography has been applied, to construct six Doppler tomograms for single orbital cycles spanning the four days of observations to support our conclusions. Our results indicate that EX Hya has a well formed disc and that the magnetosphere should extend only to about 3.75 RWD.
0035-8711
1576-1589
Echevarria, Juan
783b79d8-1f9f-4801-a79c-718d57b3a3b0
Ramirez-Torres, Abdiel
8db230bd-8c1b-48b2-9ba7-6687fd7739eb
Michel, Raul
44ee4d0c-7065-47be-ac7f-5f1b1572579d
Hernandez Santisteban, Juan
115e9657-d594-487b-b871-5c61cc32f692
Echevarria, Juan
783b79d8-1f9f-4801-a79c-718d57b3a3b0
Ramirez-Torres, Abdiel
8db230bd-8c1b-48b2-9ba7-6687fd7739eb
Michel, Raul
44ee4d0c-7065-47be-ac7f-5f1b1572579d
Hernandez Santisteban, Juan
115e9657-d594-487b-b871-5c61cc32f692

Echevarria, Juan, Ramirez-Torres, Abdiel, Michel, Raul and Hernandez Santisteban, Juan (2016) A radial velocity study of the intermediate polar EX Hydrae. Monthly Notices of the Royal Astronomical Society, 461 (2), 1576-1589. (doi:10.1093/mnras/stw1425).

Record type: Article

Abstract

A study on the intermediate polar EX Hya is presented, based on simultaneous photometry and high dispersion spectroscopic observations, during four consecutive nights. The strong photometric modulation related to with the 67-min spin period of the primary star is clearly present, as well as the narrow eclipses associated to the orbital modulation. Since our eclipse timings have been obtained almost 91,000 cycles since the last reported observations, we present new linear ephemeris, although we can- not rule out a sinusoidal variation suggested by previous authors. The system shows double-peaked H?, H? and Hei ?5876 AA emission lines, with almost no other lines present. As H? is the only line with enough S/N ratio in our observations, we have concentrated our efforts in its study, in order to obtain a reliable radial velocity semi– amplitude. From the profile of this line, we find two important components; one with a steep rise and velocities not larger than ?1000 km s?1 and another broader component extending up to ?2000 km s?1, which we interpret as coming mainly from the inner disc. A strong and variable hotspot is found and a stream-like structure is seen at times. We show that the best solution correspond to K1 = 58 ± 5 km s?1 from H?, from the two emission components, which are both in phase with the orbital modulation. We remark on a peculiar effect in the radial velocity curve around phase zero, which could be interpreted as a Rositter-MacLaughlin-like effect, which has been taken into account before deriving K1. This value is compatible with the values found in high- resolution both in the ultraviolet and X-ray. Using the published inclination angle of i = 78 ± 1? and semi-amplitude K2 = 432 ± 5kms?1, we find: M1 = 0.78 ± 0.03 M?, M2 = 0.10 ± 0.02 M? and a = 0.67 ± 0.01 R?. Doppler Tomography has been applied, to construct six Doppler tomograms for single orbital cycles spanning the four days of observations to support our conclusions. Our results indicate that EX Hya has a well formed disc and that the magnetosphere should extend only to about 3.75 RWD.

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Accepted/In Press date: 13 June 2016
e-pub ahead of print date: 16 June 2016
Published date: 11 September 2016
Organisations: Astronomy Group

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Local EPrints ID: 401582
URI: http://eprints.soton.ac.uk/id/eprint/401582
ISSN: 0035-8711
PURE UUID: 4929b069-4936-47fc-8c4b-492a7faaee8d

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Date deposited: 18 Oct 2016 14:08
Last modified: 09 Dec 2019 19:25

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