Tue, 02/06/2024 - 02:58
Tonight's astro-ph has an extensive paper describing the most recent version of the southern SkyMapper survey:
https://arxiv.org/abs/2402.02015
The survey results now appear to have much better zero-points and simply lots more data. The bright limit is about mag 9.5 in all the uvgriz filters. The consistency and general quality as described suggest it replaces APASS for the regions of the sky covered. Observers and the chart team may wish to make some comparisons.
\Brian
Brian:
I scanned/read the article and the Bessel reference. I was wondering if you had an opinion about how well the SMSS DR4 filter magnitudes transform to the Johnson Cousins BVRI filter mags, especially the B;V?
I've made some comparisons of the Atlas - Gaia - Panstarrs magnitudes and APASS magnitudes with sometimes disappointing equivalency of the BVRI transformed magnitudes! Still sometimes a few tenths mag dis-agreement.
Is Panstarrs the best equivalent (in image epoch numbers) northern survey we can use?
Ken
At least for Pan-STARRS g,r,i data, I would adopt the Kostov & Bonev transformations to BVRI:
https://ui.adsabs.harvard.edu/abs/2018BlgAJ..28....3K/abstract
In the north, and for brighter stars (Pan-STARRS saturation is around mag 13.5-14 in various filters), I would go with the ATLAS 'refcat2' (VizieR item j/apj/867/105) and adopt for now the Kostov & Bonev transformations to BVRI. refcat2 includes the APASS Chile g,r,i data (up to about +20 Dec) completely re-reduced from the raw images to ameliorate the various problems with those data.
I have written to SkyMapper project manager Chris Onken to suggest they do a match against the Stetson catalogues, since folks will inevitably ask for it, and because the zero-points and color terms for SkyMapper are shifted a bit from refcat2. SkyMapper4 has complete coverage to +16 Dec, so will have broad utility for variable star sequences.
\Brian
Brian:
I have read the same bright mag limit BUT I've found PANSTARRS catalog magnitudes brighter than 13.5, regularly as bright as 9-11.
Has the catalog been revised to provide such bright mags and if so, why has the 13.5 limit statement not been revised? What is the story?
Ken
The values brighter than mag 13.5 or certainly shown, but are often no good. Tonry's 'refcat2' catalogue was intended to remove that problem. It seems the entries are there as placeholders to show that a source exists at some location on the sky. Similar sort of thing in APASS (and elsewhere), where mag 8 or 9 stars are listed, but with 0.000 for the errors, meaning saturated images --- though sometimes they seem to be "okay" (+/- 0.05 mag say) if not great. (We really do still need a multi-color 'shallow sky' survey.) I generally compare stuff star-by-star with ASAS-3, Tycho-2, reliable single-channel photometry, and other literature sources to see how things hang together.
Meanwhile, in taking data on Landolt fields and other targets for calibration, I usually try to get stars as bright as possible in each field with the intention of getting high-weight standardized photometry for them (mostly UBV). It would be very useful to add more bright(er) stars in the existing Landolt and Stetson cluster fields using the fainter stars in the same images as reference.
\Brian
The catalogue is now query-able through VizieR as item ii/379. This will be much more convenient than the set-up at the SkyMapper site itself.
\Brian