It all comes down to array configuration. For example, if you cut the MWA at 250 wavelengths, thats basically all of the core. Many antennas would be cut completely. Heck that would be _all_ of PAPER and most of HERA. Since lofar only has a few baselines in this range, its more like the VLA. They can calibrate off of long baselines with a simple model at the cost of trading away those sensitive short baselines.
On Fri, Dec 11, 2015 at 8:42 AM, Chris Carilli <[email protected]> wrote: > for self cal of complex objects, the issue is not point sources, but how > accurately your model represents the true sky? a rough indication is the > ratio of total flux in your model vs. the total flux in a given visibility. > clearly, if your model has much less total flux than the visibility, you > are making a mistake. > > for CLEAN models, the approximation is that extended sources can be > modeled by a bunch of point sources. all of which you fold into the self > cal, but that is a detail. > > cc > > > > > > > On 12/11/2015 07:55 AM, Adam Beardsley wrote: > > From what I understood from Ger's talk in Albuquerque (and maybe I > misunderstood) was that they've always excluded some short baselines, they > are just being much more aggressive now. I don't know what they were using > previously, but the current calibration excludes baselines < 250 > wavelengths. So I wouldn't say they're just getting around to realizing > this bias, but they are being more conscience of it. > > As a side note - 250 wavelengths seems really far out there (from an MWA > background anyway). What does that do to your calibration when you're > essentially chopping all baselines that _do_ see your calibrator as a point > source? > > -Adam > > On Fri, Dec 11, 2015 at 6:37 AM Chris Carilli <[email protected]> wrote: > >> funny. leaving out short spacings in self cal is standard practice at the >> VLA since the 1980's, for the obvious reason that the model rarely >> contains all the flux density seen on short baselines. surprised they are >> just getting around to this now. >> >> do they perform the power spectral analysis on final image cubes in 3D? >> >> cc >> >> >> >> > Bonjour Heratics, >> > >> > I talked to Saleem and Leon quite a bit in Paris (supposedly, all the >> > talks >> > were filmed <http://ilp.upmc.fr/firstlight/program.php>, but only the >> > first >> > two days have been posted and that doesn't include either talk or mine). >> > Some interesting tidbits and clarifications: >> > >> > - The key improvement over previous results is that they now use only >> > the long baselines to calibrate (especially the direction-dependent >> > calibration). Before using short baselines in the direciton-dependent >> > calibration caused a loss of all diffuse structure, which got >> absorbed >> > into >> > their inferred beams. That calibration is done on every 10 seconds of >> > data. >> > >> > >> > - The LOFAR analysis strategy has been repeated iterations of >> refining >> > a >> > source model, calibrating to it, and rerunning all their analysis. >> > They've >> > done this ~10 times so far. They say it'll get a lot faster now, >> since >> > they >> > just bought a big new analysis cluster. On the other hand, the >> analysis >> > scales with the amount of data used and this limit comes from ~150 >> > hours >> > out of the ~2000 they have in the can (about 4 petabytes). >> > >> > >> > - The power spectrum error bars (e.g. on slide 25 of Ger's talk) are >> 2 >> > sigma. The power spectra really are inconsistent with noise at all k, >> > though they only go up the a relatively modest k corresponding to a >> 0.4 >> > MHz >> > binned channel width. >> > >> > >> > - Saleem showed variance statistic plots as a function of frequency, >> > both for Stokes I and Stokes V. Stokes V look at the 10ish mK level, >> I >> > at >> > the 50ish mK level. Those numbers are hard to interpret, since the >> > variance >> > statistic (both data and theory) depend on the smoothing scale in >> > frequency. He also showed a "cross RMS" which came from correlating >> > neighboring channels (on roughly the 100 kHz scale), which gave >> > slightly >> > better results (40ish mK). This is a harder statistic to interpret, >> > since >> > the correlation of EoR structure between channels on that scale is >> not >> > 100%. It seems strange to me that they wouldn't look at interleaved >> > channels, since they have so much spectral resolution at the outset, >> > but >> > they must have to bin too coarsely in frequency at some intermediate >> > stage >> > for that to work. >> > >> > >> > - Saleem said that LOFAR didn't see the wedge in their final result, >> > referring to the same slide as Ger's slide 24. Whatever their >> > systematics, >> > they must mix k_perp modes. After his talk, Saleem showed me some >> power >> > spectra with less foreground subtraction that he said had "wedge >> > structure" >> > in them. It was really hard to tell how "wedge-like" they were, in >> part >> > because they were small and over a limited k range, and in part >> because >> > they used those contours plots that are so hard to read. >> > >> > -Josh >> > >> > On Wed, Dec 9, 2015 at 11:36 PM, Saul Kohn < <[email protected]> >> [email protected]> wrote: >> > >> >> This is published online (no login required; the conference website), >> so >> >> I >> >> think it's kosher to share. Check out slides 23-25. >> >> http://lwa.phys.unm.edu/abq2015/talks/deBruyn.pdf >> >> >> >> Saul >> >> >> >> On Thu, Dec 3, 2015 at 9:12 AM, Adrian Liu < <[email protected]> >> [email protected]> wrote: >> >> >> >>> Absolutely, it’s complementary and valuable. It’s definitely a >> >>> result >> >>> that’s not just line-of-sight, and relies on foreground subtraction >> >>> at low >> >>> k’s. The foregrounds were removed using the GMCA algorithm, with 6 >> >>> components, though (understandably) during the talk they didn’t go >> >>> into too >> >>> much detail about it. (I had to talk to Ger afterwards to get the >> >>> number 6). >> >>> >> >>> Ger will unfortunately not be here on Friday, which is why he had to >> >>> present yesterday even though all the other EoR talks are on Friday. >> >>> >> >>> > On Dec 3, 2015, at 6:50 AM, Chris Carilli <[email protected]> >> wrote: >> >>> > >> >>> > well, yes and no. the number may not be much different, but, if they >> >>> are >> >>> > doing this in the image domain as well as line of sight, it shows >> >>> that >> >>> > progress can be made in 3D. that is, if the result is believable? I >> >>> would >> >>> > assume so, given they are presenting in public, but need to see >> >>> paper. >> >>> and >> >>> > maybe they are focusing on LoS PS? mantra: 'multiple approaches >> and >> >>> > experiments are good...' >> >>> > >> >>> > I will be talking about PAPER and HERA at New Mexico Tech physics >> >>> dept >> >>> > today at 4PM, for those in ABQ who might be bored and want to take >> >>> the >> >>> > drive... >> >>> > >> >>> > I will be in ABQ friday and will try to get some info from Ger. >> >>> > >> >>> > cc >> >>> > >> >>> > >> >>> > >> >>> >> as i mentioned earlier, saleem said that the limits were >> >>> "PAPER-like", >> >>> so >> >>> >> nothing revolutionarily new... he also mentioned moving back to >> the >> >>> power >> >>> >> spectrum statistic, in lieu of the variance, since the foregrounds >> >>> were >> >>> >> easier to deal with... >> >>> >> >> >>> >>> On 03.12.2015., at 14.30, Adam Beardsley >> >>> <[email protected]> >> >>> >>> wrote: >> >>> >>> >> >>> >>> mK >> >>> >>>> On Thu, Dec 3, 2015 at 6:30 AM Jonathan Pober >> >>> >>>> <[email protected]> wrote: >> >>> >>>> 20 or 30 mK or mK^2? >> >>> >>>> >> >>> >>>>> On Wed, Dec 2, 2015 at 11:47 PM, Adrian Liu <[email protected] >> > >> >>> >>>>> wrote: >> >>> >>>>> Yes. They have both P(kperp,kpara) limits as well as P(k) >> limits. >> >>> No >> >>> >>>>> mention of the variance method today. >> >>> >>>>> >> >>> >>>>>> On Dec 2, 2015, at 9:42 PM, danny jacobs >> >>> <[email protected]> >> >>> >>>>>> wrote: >> >>> >>>>>> >> >>> >>>>>> But this is a power spectrum limit rather than with the >> variance >> >>> >>>>>> method? >> >>> >>>>>> >> >>> >>>>>>> On Wednesday, December 2, 2015, Saul Kohn >> >>> <[email protected] >> >>> > >> >>> >>>>>>> wrote: >> >>> >>>>>>> Hi all, >> >>> >>>>>>> >> >>> >>>>>>> To follow this up, Ger made a LOFAR EoR project overview >> >>> >>>>>>> presentation (probably the same one as Dave was mentioning) in >> >>> >>>>>>> Albuquerque this afternoon. >> >>> >>>>>>> >> >>> >>>>>>> They were hazy on the details of power spectrum estimation >> from >> >>> >>>>>>> their images, but he quoted *preliminary* limits of between 20 >> >>> and >> >>> >>>>>>> 30mK for redshifts 7.5 to 10, k~0.05 Mpc^-1 using 155 hours of >> >>> data. >> >>> >>>>>>> Their estimate on systematics comes from Stokes V, which was >> at >> >>> >>>>>>> levels ~ 10mK, so intersecting with the higher-power EoR >> >>> models. >> >>> On >> >>> >>>>>>> the slide it quoted "Zaroubi et al. 2016", so I guess we can >> >>> expect >> >>> >>>>>>> to see something official next year. >> >>> >>>>>>> >> >>> >>>>>>> Saul >> >>> >>>>>>> >> >>> >>>>>>>> On Wed, Nov 11, 2015 at 5:06 PM, DAVID DEBOER >> >>> >>>>>>>> < <[email protected]>[email protected]> wrote: >> >>> >>>>>>>> To clarify a bit, I’m not sure that Michiel’s >> >>> statement >> >>> applies >> >>> >>>>>>>> to anything new, but rather that there was some possibility >> >>> that >> >>> >>>>>>>> Ger had made a presentation somewhere regarding a limit. >> >>> >>>>>>>> >> >>> >>>>>>>> Dave >> >>> >>>>>> >> >>> >>>>>> >> >>> >>>>>> -- >> >>> >>>>>> Sent from Gmail Mobile >> >>> >> >> >>> > >> >>> > >> >>> > >> >>> >> >>> >> >>> >> >> >> > >> >> >> >> > -- National Science Foundation Fellow Arizona State University School of Earth and Space Exploration Low Frequency Cosmology Phone: (505) 500 4521 Homepage: http://loco.lab.asu.edu/danny_jacobs/
