I think that's what Danny was saying - for HERA, the radius of the array isn't 250-wavelengths. So the inner-most dishes simply wouldn't be included. I don't think that's a problem for lofar - I'm sure every antenna has a correlation with another > 250-wavelengths. But it would be nice to see some kind of metric of how many baselines are included for each antenna...
On Fri, Dec 11, 2015 at 9:03 AM Chris Carilli <[email protected]> wrote: > not sure what you are saying. the point is not that you don't use the > core antennas in the selfcal, just that you don't use the core baselines. > you still use the core antenna correlations with the outriggers, as long as > they are long enough. of course, if even the core to outrigger baselines > are shorter than the cutoff, then indeed, you are done. and there is the > question of whether you have enough baselines to get good solutions. > > > > On 12/11/2015 08:48 AM, danny jacobs wrote: > > 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]> >>> 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]> >>> 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]> 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/ > > >
