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Hi all,

I would like to ask your opinion concerning my measurements of heliocentric radial velocity in IRAF. According to my supervisor, the values of heliocentric radial velocity of iota Herculis which I measured (I used archive data from Elodie) are totally different from previous researches and she asked me to check again the method of HRV measurement. I would like to verify whether my method of HRV measurement is correct or not. Below are the step by step which I did:

1) I started my measurement by normalizing the spectrum using continuum routine. Then using scopy routine, I chose the range of wavelength that I want to study. For my case, I chose Sulfur II (rest wavelength 5453.810 A). Data from Elodie only gave instrumental flux in y-axis. The data is wavelength calibrated by the Elodie observer.

2)Then I key in all the information for observatory (observatoire de haute province) to compensate the Earth's motion

latitude: 43.9308 N
longitude: 354.2867 (IRAF measure longitude from West Greenwich)
UTC: +1
altitude: 650m

3) After that, I use rvidlines routine to measure the heliocentric radial velocity. I put the measured wavelength in the klines.dat. The value of heliocentric radial velocity is given by Vhelio in the IRAF. Here, I also attached the logfile from IRAF

I hope you can give me some advices.

Thank you

# RVIDLINES: Observatory parameters for OHP
# latitude = 43.94
# longitude = 354.2900000000001
# altitude = 650.

Wed 15:37:57 03-Apr-2013
Features identified in image 19950517_0009Sulfur - Ap 1: HD160762
Measured User Residual Velocity Residual Wt Label
5453.446 5453.446 0. 4.6753343 0. 1.00

19950517_0009Sulfur 1 : Zobs = 7.0794E-7, Mean err = 0., Lines = 1
19950517_0009Sulfur 1 : Vobs = 0.21223 km/s, Mean err = 0. km/s, Lines = 1
19950517_0009Sulfur 1 : Zhelio = 1.5595E-5, Mean err = 0. km/s, Lines = 1
19950517_0009Sulfur 1 : Vhelio = 4.6753 km/s, Mean err = 0. km/s, Lines = 1
19950517_0009Sulfur 1 : HJD = 2449855.379616933

Just a guess, but it appears the Elodie data are wavelength corrected to the solar system barycenter already (from the archive page, but with no real confirmation). This means that the observed velocity needs to have the barycentic correction removed in order the get back to the heliocentric velocity, i.e.

VHelio = Vobs - Vsolar

The Vobs value you get from the RVIDLINES measurement, Vsolar you can get from the RVCORRECT task. So for this object we have



and Vhelio = 0.21223 - 19.158
Vhelio = -18.94577

which is much closer to the Simbad value of the radial velocity for the object.

Thank you Dr Mike.