Unusual long-term variables found in DASCH

The most exciting new science from DASCH will be long-term variables. We have found hundreds of new unusual long-term variables from partial analysis of about 5000 scans. Some of them do not match any of the common classes, and may instead suggest extremely short-lived evolutionary stages. Click on the left three examples which were featured in a poster paper at the IAU XXII General Assembly in Rio de Janeiro in August, 2009 . According to their spectra, they are all ~K2 giants, but not R Coronae Borealis stars. Their nature remains unknown.

Sample DASCH lightcurves

A paper has been submitted with a description of the photometry pipeline.

Click on the thumbnail to the left to view the entire output of the photometry pipeline using the eclipsing binary RY Cancri as an example. This lightcurve contains 1042 measurements of brightness obtained over 104 years. The plot uses the GSC2.3.2 designation N2312220105 for this variable. The star's magnitude (brightness) is plotted against time (first panel) and chronological plate sequence (second panel). The third panel shows in black the spatial bin of the image from bin 1 at the center to bin 9 at the edge; and in red the number of local calibrators to determine the image's local correction of irregular spatial variations in plate sensitivity. The fourth panel is used to verify that the star's variability does not come from image saturation effects. The fifth panel shows the local calibration error. Finally, the sixth panel shows the difference between magnitudes with (black) and without (red) local calibration. A description of plotting symbols appears at the bottom of this page.

We have the option of removing all but the good points as shown by the lightcurve on the left. Note the faint points below the rest, which correspond to eclipses of the primary star by its fainter companion.

Here is the lightcurve of RY Cancri folded at its known binary period of 1.092943 days, to show the eclipse. The light-curve is plotted over two cycles, the first cycle shows estimated error bars for each point.

For quality control purposes we are also interested in stars that do NOT vary. Such constant-brightness stars enable sensitive determination of various systematic effects and provide a completely independent measure of uncertainties. At left is the lightcurve of such a star demonstrating about +/-0.1mag photometry over 600 plates, that span 100 years and 19 different plate-series.

Plotting Symbols

The following plotting symbols are used:

Solid circle

for a good point

Small solid circle

for a good point at the edge of the plate

Open circle

for a large error point

Small open circle

for a large error point at the edge of the plate

Arrow pointing down

for not found at the indicated limiting magnitude

Small arrow pointing down

for not found at the edge of the plate

Asterisk

for a suspected plate defect

Triangle

for a high astrometric error object

Open square

for a Pickering Wedge object

Solid square

for an object with high or unknown extinction

Arrow pointing up

for an object too bright for the photometric algorighm

Diamond

for a blended object

Cusped square

for a high local correction object

Letter c

for a good object without color correction