3. Radial velocities

A cross-correlation technique was used to calculate the radial velocities of the observed RR Lyrae. As a first step, the original wavelength range was logarithmically rebinned from 4189.4 to 4389.4 Å for Calar Alto spectra and from 4073.6 to 4446.7 Å for Sutherland spectra to 1024 and 2048 data points respectively. After this, the spectra were cross-correlated (using a Fast Fourier Transform technique) against the observed IAU radial velocity standards (Table 1 (click here)). A 5% cosine-bell was used to remove the start and end spectrum discontinuities. The cross-correlation peak was then fitted to a parabola, the maximum value of the parabola being the radial velocity difference between the standard and the target star. Finally, the heliocentric correction was applied using the standard IRAF package.

The phases of our observations were calculated using the published periods from the GCVS and an arbitrary zero-point. Systemic velocities were then determined by fitting these phased radial velocity measurements for each star to the ``standard" RRab Lyrae radial velocity curve given by Liu (1991). A free parameter in the Liu curve is the amplitude. Liu found 22 RRab Lyraes with published radial velocity curves and these have a mean amplitude of 61.5 with an rms scatter of 8.4 . Liu shows that there is a correlation between light curve amplitude and velocity amplitude; however, since the light curve amplitude is not known for many of the stars in our sample, we have used the mean amplitude of 61.5 to construct the ``standard" curve. Amongst the stars for which we have three well-phased spectra with good S/N there are 4 RRab Lyraes and 2 RRc Lyraes with complete radial velocity curves available in the literature. Comparing our values of the systemic velocity with the literature values for the 4 RRab Lyraes showed a mean difference of 1.7 and an rms difference of 3.1 . For the RRc Lyraes, where the velocity amplitude is smaller and the velocity curve more symmetric, we determined the systemic velocity by simply taking a mean of our three measurements. Again, comparing our systemic velocities with the literature values showed, for the two RRc Lyraes, a mean difference of 1.5 and an rms difference of 2.1 .

Thus for those stars where we have three well-phased radial velocities and good S/N spectra, a realistic error in the systemic velocity is . For those stars with fewer measurements and/or lower S/N the errors are larger. The full list of RR Lyraes, their systemic velocities and associated errors is given in the Appendix (available electronically).

 

HR 1101 27.9

HD 65934 35.0

HR 4540 5.0

HR 5694 53.5

HR 7560 0.1

HR 8969 5.3

 

3.1. Binary candidates

Because the Horizontal Branch is a relatively short-lived phase of stellar evolution, most companion stars will be much fainter than the RR Lyrae itself, i.e. the companions will either be low-mass main sequence stars or white dwarfs. In general, therefore, the only methods available to detect companions are to look for variations in either the time of maximum light or the systemic velocity. In Table 2 (click here) we list those RR Lyraes which show significant differences between our values and previous values of the systemic velocity. Examination of the spectra of these stars showed no evidence of line doubling for any of them.

The only one of stars included in Table 2 (click here) previous suspected to be a member of a binary is TU UMa. Saha & White (1990), using published times of maximum light, calculated the orbital parameters for TU UMa and our value of the systemic velocity is not inconsistent with their prediction. For the other stars, a literature search showed there were insufficient published times of maximum light to attempt an orbital solution and clearly it would be of value to place these stars in a long-term observing programme in order to acquire these data.

 

This work Previous work

BX Dra -24 3 9

XX Hya 32 30 9, 14, 16

BX Leo -7 15 16

CN Lyr 13 20 9, 16

TU UMa 96 3 1, 8 12, 16

 

 

HR 0033 6254 -0.21(9)

HR 0033 6346 -0.27(7)

HR 4540 6060 +0.16(5)

HR 4540 5973 -0.04(6)

HR 4540 6095 +0.09(5)

HR 5694 6278 -0.11(8)

HR 5694 6102 +0.02(7)

HR 5694 6113 +0.04(7)

HR 5694 6258 +0.06(6)

HR 5694 6140 +0.00(6)

HR 5694 5950 -0.16(6)

HR 7560 6231 +0.15(7)

HR 7560 6190 -0.10(5)

HR 7560 6188 +0.19(6)

HR 7560 6132 +0.13(6)

HR 7560 6060 +0.08(6)

HR 8969 6205 -0.06(8)

HR 8969 6184 -0.15(5)

HR 8969 5991 -0.19(6)

HR 8969 6021 -0.15(6)

HR 8969 6258 -0.11(6)

1: Edvardsson et al. (1993); 2: Bell et al. (1994); 3: Alonso et al. (1996); 4: Sokolov (1995); 5: Borges et al. (1995); 6: Cayrel de Strobel et al. (1992); 7: King & Boesgaard (1995); 8: Carney et al. (1987); 9: Favata et al. (1996); 10: Tomkin et al. (1995); 11: Blackwell et al. (1994); 12: Drake & Laming (1995).  

 

SW And 47116.185+0.442266³ 0.86 5921 -0.36 (6)

AE Boo 30388.203+0.314892² 0.20 6616 -0.95 (4)

AE Boo 0.59 6296 -1.18 (3)

AE Boo 0.28 6978 -0.99 (3)

AE Boo 0.94 6796 -0.96 (3)

RS Boo 46948.720+0.377337¹ 0.47 6233 -0.31 (4)

RS Boo 0.87 6210 -0.34 (4)

RR Cet 46773.724+0.553038¹ 0.65 6000 -1.24 (2)

SU Dra 46833.664+0.66042¹ 0.67 5721 -1.97 (5)

SU Dra 0.99 7200 -1.42 (2)

SW Dra 46495.754+0.569669¹ 0.30 6190 -0.70 (4)

SW Dra 0.00 7279 -0.84 (2)

XX Hya 39832.011+0.507741² 0.40 6839 -1.22 (2)

TT Lyn 46773.679+0.597436¹ 0.74 5888 -1.27 (2)

TT Lyn 0.41 6223 -1.38 (4)

CN Lyr 44486.334+0.411382² 0.09 6582 -0.09 (2)

CN Lyr 0.40 6173 -0.10 (2)

KX Lyr 39630.870+0.440904² 0.20 6368 -0.30 (1)

KX Lyr 0.46 6248 -0.41 (3)

DH Peg 44463.571+0.255510² 0.26 7285 -1.35 (1)

DZ Peg 33891.308+0.607344² 0.41 6400 -1.21 (3)

VZ Peg 38317.293+0.306486² 0.54 7010 -1.63 (3)

AR Per 46773.473+0.425549¹ 0.24 6560 -0.23 (2)

AR Per 0.48 6143 -0.23 (3)

AP Ser 6475 -1.62 (3)

VY Ser 38466.244+0.714096¹ 0.24 6101 -1.46 (2)

VY Ser 0.62 5869 -1.42 (2)

T Sex 46833.592+0.324712³ 0.32 6650 -1.30 (3)

T Sex 0.62 7200 -1.27 (2)

T Sex 0.32 6737 -1.25 (2)

SX Uma 6563 -1.75 (1)

SX Uma 7342 -1.51 (1)

1: Fernley & Barnes (1996); 2: Kholopov et al. (1990); 3: Liu & Janes (1990).  

 

TY Aps 0.39 6194 -0.92 (4)

XZ Aps 28715.330+0.587434¹ 0.93 6579 -0.55 (8)

BV Aqr 37524.218+0.364048¹ 0.62 7011 -1.16 (3)

BV Aqr 0.09 6868 -1.22 (3)

BV Aqr 0.43 6394 -1.20 (5)

BV Aqr 0.94 7138 -1.15 (1)

RR Cet 46773.724+0.553038³ 0.77 6044 -1.29 (5)

RR Cet 0.45 5979 -1.38 (4)

RR Cet 0.26 6116 -1.29 (6)

DX Del 39367.340+0.472617¹ 0.21 6799 -0.31 (5)

DX Del 0.48 6141 -0.38 (8)

DX Del 0.59 6041 -0.41 (6)

CS Eri 38417.087+0.311331¹ 0.12 6928 -1.36 (4)

CS Eri 0.31 6679 -1.45 (4)

XZ Gru 38260.438+0.34741¹ 0.68 6158 -1.37 (6)

XZ Gru 0.03 6068 -1.12 (5)

XZ Gru 0.43 6029 -1.36 (7)

IK Hya 38461.510+0.65¹ 0.25 6373 -1.24 (1)

FW Lup 42171.377+0.4841712¹ 0.80 6506 -0.11 (7)

FW Lup 0.14 6405 -0.26 (9)

FW Lup 0.36 6294 -0.14 (7)

FW Lup 0.47 6164 -0.27 (10)

VY Nor 25535.249+0.375305¹ 0.63 6000 -2.01 (1)

VW Scl 27809.381+0.510915¹ 0.15 7121 -0.84 (4)

VY Ser 38466.244+0.714096 0.82 6024 -1.30 (6)

VY Ser 0.21 6335 -1.53 (3)

VY Ser 0.54 5969 -1.65 (2)

MT Tel 42206.35+0.316897¹ 0.57 6832 -1.64 (2)

MT Tel 0.92 7085 -1.62 (2)

AM Vir 26859.275 +0.615089¹ 0.12 6493 -0.74 (6)

AM Vir 0.20 6037 -1.11 (5)

AM Vir 0.53 5932 -1.30 (1)

UU Vir 46878.822+0.475606² 0.31 6359 -0.70 (7)

1: Kholopov et al. (1990); 2: Jones et al. (1988); 3: Fernley & Barnes (1996).