History of TRES Zero Point

Figure 1, a history of the five "standard" stars (HD 115404, HD 182488, HD 3765, HD 38230, and HD 65583), is presented below. Radial velocities for each star are binned by run. These are all multi-order velocities, relative to a template observation. Two of these stars show a known, long-term drift: HD 115404 and HD 182488. The drift in H115404 is not well understood or documented, so its use as a standard star may be discontinued. The drift in H182488 is well defined and can be approximated as the straight line RV = 415.02 - 0.0075*(JD-2400000) m/s. This drift has been removed from the points plotted in Figure 1.

Figure 1:

Figure 2 shows the recent history of the zero point, starting at the time when Gabor installed the new and improved fiber front end and the spread in the radial velocities drastically decreased. Error bars are the standard deviation of the mean for each run.

Figure 2:

Below is a list of known incidents that could cause a shift in zero point:

2010-12-18 2455547 JD New front end and fiber feed

2011-07-07 2455750 JD New dewar lens

2012-02-23 2455981 JD New shutter installed

2012-03-26 2456013 JD Positioner disabled ~30 Mar ??

Files containing the mean radial velocities to be used for multi-order zero point corrections from each "standard" are provided below

H115404.rvbyrun H182488.rvbyrun H3765.rvbyrun H38230.rvbyrun H65583.rvbyrun

To update these files, and get an updated version of these plots, run the IDL program update_stands.pro. Instructions and requirements are described in the comments at the beginning of the .pro file.

An example of a script that can be used to correct a ccfSum.txt file by one of the .rvbyrun files and create a .orbpl file is star_correct.pro.