Spectroscopy was performed with the G430L, G430M, and G750M gratings as detailed in Table 1, using default STIS dither patterns along the slit, and achieving average resolutions of 6.8, 0.7, and 1.4 Å, respectively.
The individual spectral images were first shifted on to a common frame as indicated by the image header astrometry and using integer pixel shifts.
This ambient light correction resulted in flux measurement changes less than 1.2 per cent for the five filters below 5000 Å, but rose to around 4 per cent for the three longer wavelength filters.
The measured fluxes for GJ 86B are listed in Table 2.
The contrast between the peak signals from the science target and the primary diffraction spikes was 17:1 at the lowest in the G750M observations, and at least twice as high in the region of the science spectrum.
Combined-frame STIS CCD spectral images of GJ 86B taken in three gratings, with wavelength increasing to the right.
This sequence employed the default UVIS dither pattern with four points in a parallelogram, and was repeated four times for a total of 16 exposures.
Both primary and secondary star were well detected in this first set of exposures, and in the linear response regime with high signal-to-noise ratio (S/N) Immediately following the short-exposure sequence, a single dither pattern of four deeper exposures was executed in each of eight filters (see Table 1 and Fig. At the phase II design stage, the brightness of the companion was poorly constrained and the longer exposures were to insure high S/N photometry [up to the limit imposed by the point spread function (PSF) wings of the primary] at all wavelengths.
In order of discovery, these planetary systems are GJ 86 (HR 637, HD 13445) (Queloz et al. Subsequently, the distant companion was directly detected at a projected separation of 1.7 arcsec, but 9 mag fainter than the primary in the band (Els et al. The companion, GJ 86B, was later imaged by Mugrauer & Neuhäuser (2005) and Lagrange et al.
The similarity of GJ 86 and Procyon prompted a re-analysis of the white dwarf in the latter system, with the tentative conclusion that Procyon hosts a planetesimal population. However, only in GJ 86 is the stellar secondary a white dwarf rather than a second main-sequence star, and the Jovian planet thus orbits the originally massive component.
The periastron distance in Procyon is 20 per cent smaller than in α Cen AB, but the metal-enriched atmosphere of Procyon B indicates that the planet formation process minimally attained 25 km bodies, if not small planets as in α Cen. Furthermore, the initial binary separation was smaller, making GJ 86 a challenging environment in which to form planets.
Fortunately, even without stray light correction, the dither-combined image sets yielded S/N 60 east of north, and each frame is 8 arcsec on a side.
The bottom right-hand image is a composite RGB frame using the F225W (blue), F275W (green) and F336W (red) filters.
All five of these binaries are thought to have ≲ 30 au and a giant planet orbiting the primary star.