What has been described thus far is the final state of affairs. As my thesis was a learning process, the procedures and survey itself evolved between 2007 and 2010.
As briefly mentioned in§4.1.4, the first half of the southern sky (extracted by Dr. Henry) was extracted using a different set of color-color selection boxes that came very close to the giant locus at the blue end of the M dwarf sequence. While this was eventually changed to the current set of boxes, the targets that were now excluded remain in an “outside the boxes” section of the master list (note the small group of open points around (1.0,4.5) in Figure 4.6). The second half of the search (done by myself in 2009) used the final set of color-color selection boxes the entire way through.
Originally, my thesis dealt with all of the stars found in the TINYMO survey, as a result many higher proper motion objects within 15 pc were also within my purview. This definition changed in 2010 to include only stars with proper motions less than 0.18′′
yr−1; the
donated to other research samples5; it is because of work on those other samples that Table
4.3 includes so many results for those objects. In return, I gained claim over several CTIOPI astrometry targets not found in the TINYMO search that were nevertheless moving slower than 0.18′′ yr−1. In general, these objects are hotter spectral types than M2 (removed by
color cut), cooler than M6 (removed by the merger with the giant branch), outside the spatial range of the southern hemisphere we searched, or beyond 15 pc by CCD photometric distance estimate. Some are harder to explain, though; they may have been thrown out by ellipticity, quality, or the 4-plate-detection requirements in the first stage of the SuperCOSMOS search. By the same token, the 15 pc distance limit was settled upon in 2009. Prior to this, all the stars in the first half of the search with plate distances less than 12.5 pc had been added to the parallax observing list, while the intention was to get photometry for all of the “X- ray” and “good” samples (which would have placed an inordinate drain on our photometry program). Thus, when the distance limits were imposed, several stars with plate distances greater than 15 pc had nevertheless been observed for CCD photometry, and found to have CCD distances within 15 pc, and were added to the program. This biased the sample toward stars from the first half of the TINYMO search, and is partially responsible for our interest in getting photometry for all the X-ray bright targets.
Several promising targets were added directly to the photometry and parallax observing lists in 2007 and 2009. These targets were typically (but not always) X-ray bright and had predicted distances close to 10 pc. Spectroscopy was only started in 2009, and was not used to keep targets off the observing programs until 2010. Fortunately, there were only a handful
of cases where giants were accidentally observed for parallax. Only two – SCR 0747-5412 and SCR 0833-6107 – were observed for long enough to attempt a parallax reduction; the rest were kicked off after one or two observing sessions. This caused a problem for the photometry program when the Mira variables turned out to vary greatly from run to run, and initially caused our photometrists to throw out entire nights6 of good data.
The spectroscopic goals changed over the course of the project. Several stars that did not meet our later 15 pc/9 plate distances criteria – including both our Carbon stars (§5.8) – were observed in the early days of our spectroscopy program. Several known giants were intentionally observed to provide comparisons. 10 targets were observed by Stella Kafka on the CTIO 4m in February 2008, prior to our commitment to do spectroscopy ourselves. Those spectra are higher resolution than later CTIO 1.5m spectra, and cover 4900˚A– 8050˚A, omitting both Na I and Ca II features we normally used to identify spectra.
Finally, the X-ray sample was originally defined by SIMBAD rather than VizieR’s ROSAT All-Sky survey catalogs; in this way my X-ray bright sample originally included several targets that either had high X-ray error or were too far from an X-ray source to ultimately qualify as a detection. This original list, from the first half of the search, was the one sent to HST in 2008.
4.2.1 A Commentary on the Design Decisions
Some time has passed since the initial survey was done; and in that light there are changes that would be made if the survey were attempted now:
• The initial survey relies greatly on the epoch spreads of the individual plates to set its upper limit. This information was in the SuperCOSMOS output but was never checked to make sure the survey would reasonably contain all stars with proper motions as large as 0.18′′ yr−1- this could be done with an age-map to pinpoint areas of larger epoch
spreads. Nigel Hambly has more recently provided an extra sift of the database for the obvious case of the region between 0 DEC and −20 DEC where older POSS-I E R1 plates were used, to complete proper motions up to 0.18′′ yr−1. This extra list –
EXTRMO – was never added to the thesis.
• If a single color was erroneous, up to 5 color relations could have been wrong. Using this logic, Finch et al. (2007) and Boyd et al. (2011a) both accepted objects with as few as 6 matching color relations, rather than the 9 I selected here. Given that the only colors in five relations were BJ and R2, the most useful way to do this would be
to determine if the failed color relations all involve one specific filter.
• The regions of sky around the North Galactic Spur were probablynottoo contaminated to deal with.
• The X-ray error cutoff (25%) was chosen arbitrarily.
• I did not take proper motion into account when searching literature sources that listed no proper motion themselves. With the General Catalog of Variable Stars (GCVS Samus et al. 2012), and the Catalog of Galactic Carbon Stars (CGCS Alksnis et al. 2001), no epoch of observations were included, so no proper motion sliding could be
done. The ROSAT All-Sky catalogs were built from observations taken in 1990 and 1991; fortunately, sliding stars to epoch 1991 made no change in the X-ray detections (not that it should have, the fastest-moving object in the TINYMO survey (0.444′′yr−1)
only moved 4′′ in 9 years).