Measurement Of Stellar Radial Velocities Utilizing Amateur Astronomical Equipment

Daniel Del Proposto

Willow Creek Observatory

February 23, 2002

Abstract

To explore the measurement of stellar radial velocities using specific amateur astronomical equipment, allowing the amateur astronomer to generate accurate scientific results that fall within the published radial velocity requirements for a specific star or other extended object. The equipment utilized are a ST-7 CCD Camera and Self Guiding Spectrograph, both manufactured by Santa Barbara Instrument Group (SGS). The instruments are integrated together and attached to an Ultima 8 PEC Telescope manufactured by Celestron International.

Table of Contents

Abstract ............................................................................……………….................…. 2

Table of Contents .....................................................................................…………….. 3

List of Figures ...........................................................................................……………..4

List of Tables.............................................................................................……………..5

Measure Of Stellar Radial Velocities Utilizing Amateur Grade

Astronomical Equipment ...............................................................................………….6

References ............................................................................................……………… 12

List of Figures                                                                                           Number  Page

Figure 1  Spectrum of 53-Kappa Orionis January 24th 2002 ....................…………….8

Figure 2  Spectrum of 53-Kappa Orionis January 25th 2002 ....................…………….9

Figure 3  Spectrum of 53-Kappa Orionis February 13th 2002 ...................…………...10

Figure 4  Spectrum of 53-Kappa Orionis February 17th 2002 ...................…………...11

List of Tables                                                                                           Number Page

Table 1 Results of the measurement of radial velocities of 53-Kappa Orionis .......……. 6

Table 2 Technical specifications of Self Guiding Spectrograph (SGS) .................…… 13

Table 3 Technical specifications of Celestron Ultima 8 PEC Telescope ...............…… 14

Table 4 Technical specifications of SBG ST-7 Imaging Camera ......................………. 15

Measurement Of Stellar Radial Velocities Utilizing Amateur Astronomical Equipment

 Astronomical spectroscopy is relatively new to amateurs and has just recently become affordable for the amateur astronomer. Utilization of an amateur telescope and spectrograph make it is possible for the amateur to perform quality scientific endeavors. One such endeavor is the measurement of radial velocities using a high quality commercially manufactured spectrograph.

 Four spectra were collected from 53-Kappa Orionis, located in constellation Orionis, over a period of three weeks and analyzed to determine radial velocities. The instrument configuration was identical for all samples taken. The Self Guiding Spectrograph (SGS) is connected to the ST-7 CCD Imaging camera. The SGS with ST-7 CCD Imaging Camera is then attached to the telescope, a Celestron Ultima 8 PEC.

The focal ratio of the telescope is F/6.3 using a Celestron F/6.3 focal reducer. A mercury vapor spectrum analysis tube and power supply from Edmund Scientific was used for line calibration. The spectrum of the star and calibration source was taken at the same exposure for accurate spectrum calibration. Radial velocities were measured using two software packages. The first package, Spectra (Version 1.2) was written by Alan Holmes of SBIG. The second software package used, Visual Spec (Version 2.0.6), written by Valerie Desnoux, was used for correcting radial velocities to compensate for Earth’s orbital velocity and verification of line measurements performed with Spectra.

The results of the radial velocities are accurate when taking into account the published instrument accuracy of +-6 km/sec as stated by SBIG. The following table delineates the results of my analysis of the spectra for radial velocities.

 

Table 1

Results of measured radial velocities of 53-Kappa Orionis

 

Object	Observed Radial Velocity	Published Radial Velocity	Spectrograph’s accuracy
53-Kappa Orionis (1/24/2002)	+15.21 km/sec	+21 km/sec	+- 6 km/sec
53-Kappa Orionis (1/25/2002)	+15.53 km/sec	+21 km/sec	+- 6 km/sec
53-Kappa Orionis (2/13/2002)	+23.19 km/sec	+21 km/sec	+- 6 km/sec
53-Kappa Orionis (2/17/2002)	+21.01 km/sec	+21 km/sec	+- 6 km/sec

 

The published radial velocity of +21 km/sec is assumed accurate (Garrison, 2002). The results above positively establish that amateur astronomy equipment, and specifically the SGS can be used to identify and measure stellar radial velocities.

Figure 1

Spectrum of 53-Kappa Orionis, January 24^th 2002

Spectrum of 53-Kappa Orionis taken on January 24th 2002 with SBIG SGS at high resolution. The exposure time is 1800 seconds. The calculated radial velocity is +15.21 km/sec and is well within the published accuracy of the instrument of +- 6 km/sec and therefore very close in value to the published radial velocity of this star +21 km/sec