bcvcorr: Compute radial velocity correction to solar system barycenter

Package: rvsao

Usage

bcvcorr image

Parameters

# Spectra

spectra "": List of input spectra

specnum "0": Spectrum number(s) if multispec file. This affects how the barycentric velocity will be written into the header if savebcv is yes. If specnum is 0, the BCV keyword is used; otherwise, APVELn is used, with the barycentric velocity correction in the 4th field: 0.0 0.0 _ bcv .

specdir "": Directory for input spectra

specsky no: If yes, this spectrum is a twilight sky or solar spectrum, and the velocity correction is computed from the direction of the sun, not the telescope pointing correction.

subgrav no

If subgrav=yes and specsky=yes, subtract a correction for the sun's gravity (0.636) from the barycentric and heliocentric corrections computed by the program. If savebcv=yes, BCV, HCV, and SGRV are written to the image header. HCV, the velocity of the sun relative to the spectrograph with the gravitational correction subtracted, should be used as the spectrum correction (rvsao.svel_corr=heliocentric) when cross-correlating twilight spectra with XCSAO. # Sky direction

keyra "RA": Right ascension header keyword

keydec "DEC": Declination header keyword

keyeqnx "EPOCH": Coordinate equinox header keyword

keyjd "HJD": Header keyword for Julian date at middle of observation

keydate "DATE-OBS": Header keyword for date of observation (dd/mm/yyyy)

keystart "UTOPEN": Header keyword for UT at start of observation

keymid "UTMID": Header keyword for UT in middle of observation

keyend "UT": Header keyword for UT at end of observation

keyexp "EXPOSURE": Header keyword for duration of observation in seconds

obsname "file": Observatory name. If file to read from image header

keyobs "SITENAME": Observatory name header keyword

keylat "SITELAT": Observatory latitude header keyword

keylong "SITELONG": Observatory longitude header keyword

keyalt "SITEALT": Observatory altitude header keyword

obslong 0.0: Observatory longitude, used if obsname is not "file"

obslat 0.0: Observatory latitude, used if obsname is not "file"

obsalt 0.0: Observatory altitude in meters, used if obsname is not "file"

savebcv no: Save barycentric velocity correction as BCV and heliocentric velocity correction as HCV in data file header (yes or no)

savejd no: Save Geocentric Julian Date as GJDN, Heliocentric Julian Date as HJDN, and UT midtime of observation as UTMID in data file header (yes or no)

verbose yes: Displays heliocentric and barycentric corrections

printmode 1: If 1, display heliocentric and barycentric corrections and ancillary data; if 2, display only barycentric correction

debug no: Displays intermediate results

Description

bcvcorr can be used to set the barycentric velocity correction of spectra which do not have the header keywords expected by the correction computation subroutine in XCSAO, EMSAO, or SUMSPEC, or use different keywords than the program expects. The time, date, direction, and observatory can come from specified keywords or values directly from parameters. In the case of the observatory position, a third option is to set the obsname parameter to a string which is looked up in the IRAF observatory database. Either keymid or two of keystart, keyend, and keyexp will be used to compute the exact observation time, in conjunction with the date from keydate, if keyjd, which is assumed to be the midtime of the observation, is not present. If savebcv is yes, the barycentric velocity correction is written to the image header. If specnum is 0, the BCV keyword is used; otherwise, APVELn is used, with the barycentric velocity correction in the 4th field: 0.0 0.0 _ bcv . No matter what specnum is set to, the midtime UT is written to UTMID, and the Julian Date and Heliocentric Julian Date are written to GJDN and HJDN respectively, but only to those keywords which are not already filled. The barycentric velocity correction is added to the observed redshift of a spectrum to get a velocity relative to the solar system barycenter so that a set of radial velocities over time have a constant reference point.

Example

To compute a spectrum's barycentric velocity correction, reading everything from the spectrum's header:

RA      = ' 11:04:31.90'       /RIGHT ASCENSION SET BY COMMENT FILE
DEC     = '-21:07:35.0'        /DECLINATION SET BY COMMENT FILE
EPOCH   =               2000.0 /SET BY COMMENT FILE
DATE-OBS= '28/01/100'           /UT DD/MM/YY AT END OF EXPOSURE
UT      = '08:00:28'           /UT HH:MM:SS AT END OF EXPOSURE
UTOPEN  = '07:42:26'           /UT HH:MM:SS AT BEGINNING OF EXPOSURE
EXPTIME =              1081.01 /INTEGRATION TIME, SECONDS
HJDN    =        2451571.83082 /HELIOCENTRIC JULIAN DAY AT MIDDLE OF EXPOSURE
SITENAME= 'oro     '
SITELONG= '+71:33:33.0'        /LONGITUDE, DEGREES WEST OF ZERO
SITELAT = '+42:30:13.0'        /LATITUDE, DEGREES
SITEELEV=                137.0 /ELEVATION, METERS

Note that the RVSAO package recognizes nonstandard FITS dates, such as this one, which really should be '2000-01-28'.

rv> bcvcorr spectrum
0104.H096050.fits: 4096 x 2 x 1 2-D image
UT start: 7:42:26.0, mid: 7:51:26.5, end: INDEF, exp: 1081
2000-Jan-28 7:51:26.5 UT
RA: 11:04:31.9, Dec: -21:07:35.0  2000.0
28/01/100 lat 42:30:13.0 , long 71:33:33.0, alt 137.0
Julian date is 2451571.82739 at 2000-Jan-28 7:51:26.5 UT
Object at ra 11:04:31.900 dec -21:07:35.00 eq 2000
Heliocentric Julian date: 2451571.83081
gbcvel = 20.6503  ghcvel = 20.6598  geovel = -0.0394
bcv = 20.6109  hcv = 20.6204 computed
bcv = INDEF  hcv = INDEF from file

bcvcorr: Compute radial velocity correction to solar system barycenter

Usage

Parameters

Description

Example

See also