[QUOTE=
I wonder if any of IIS's experienced AP hands might try some very deep field images in the B band seeking faint emissions not recorded in existing images. Then, as per Greg Bock's excl suggestion, overlay the images on the SN and see what turns up.[/QUOTE]
Stu, et al, weather here in SE qld will be rubbish until hell freezes over i think. Maybe someone with clear skies can do a long exp. image, Stu, you're probably best placed to do this!
Greg-Trying to get data but the moon bet me for the next week or so.
Might try some HA but I broke my HA filter need another one.
Just PLEASE send some rain over here we are as dry as a crisp
There's a faint galaxy, PGC 538542, roughly 6' SSE with a NED listed z=0.003595 (subject to important NED "See essential note" caveat) and Heliocentr.radial vel. of 1078 m/sec(.....)
(.....)The locale of SN 2013aa 196 arcsec fm 5643's core (thanks again, Malc) still has me wondering how it got there.(....)
I wonder if any of IIS's experienced AP hands might try some very deep field images in the B band seeking faint emissions not recorded in existing images.
Hello, Dana,
and Greg and Malc, and others who have commented about the large separation of the supernova from the host galaxy.
In practical terms, galaxies, when imaged to very very faint isophotes, are normally much larger in diameter than the diameter that is usually seen in amateur images, and galaxies are typically much larger in diameter even than the standard D25 diameter (to 25th Blue magnitude per square arcsecond) which is given for each galaxy in the galaxy catalogues.
(( The exact outermost Radial profile of surface brightness, as a galaxy's surface-brightness decreases with progressively increasing galactocentric radius, can have several different and well-defined forms. Some galaxies have a fairly sharp cutoff in light at some diameter, while other galaxies keep on extending outwards into the field .... even beyond 28th Blue Magnitude per square arsecond)
The best source of (southern) galaxy diameters to very faint isophotes is the “Surface Photometry Catalogue of The ESO-Uppsala Galaxies”(1989) by Lauberts and Valentijn , which is also known as the ESOLV (or the ESO-LV).
This very important catalog of bright galaxies is available in electronic form, and also (perhaps!) still in a paper version from the ESO.
Like the RC3, the ESO-LV is a large and homogeneous dataset, with relatively consistent and relatively high accuracy. The ESOLV is as important for southern galaxies as the Third Reference Catalogue of Bright Galaxies (=RC3) is for the all-sky bright galaxy population.
The ESO-LV gives the following angular diameters for the Major Axis (long axis) of NGC 5643:
Standard Diameter to 25th Blue magn. per sq. arcsec : :
305 seconds of arc (= 5.08 minutes)
Diameter to 26th Blue magn. per sq. arcsec : :
380 seconds of arc (6.33 minutes of arc)
Unfortunately, the ESO-LV doesn't give a diameter for this galaxy to the even fainter level of 27th Blue magnitude per square arcsecond, but the conclusion seems quite firm that a supernova which is 196 arcseconds (3.26 arcminutes) from the centre of NGC 5643 is still plausibly within the confines of this galaxy.
Now I would be as excited as the next man (or woman) if the supernova turns out to be associated with a dwarf companion of NGC 5643, but this numerical argument puts the conservative view that the supernova does belong to the big galaxy.
Here is the DSS image taken from wikisky.org, which shows the host galaxy extending outwards a lot further than it does in the other images in this thread;
(this is far from being the sharpest version of Digitized Sky Surveys, but it shows the galaxies at higher contrast than the other versions!)
Best Regards,
from
Bad Galaxy Man
P.S.
How accurate are ESOLV diameters of galaxies? They are usually about right, but occasionally they are very wrong!!
If anything, the galaxy diameters in the RC3 are even worse, as they are simply derived from an extrapolation of the inner (radial) light profile. At least ESOLV galaxy diameters are actual measurements, rather than extrapolations, or averages of several bad data-points. Still, even ESOLV is better for statistical (large number of galaxies) work than for finding a really accurate measurement.
The only way to get a really accurate angular diameter is to do CCD surface photometry of a galaxy.
Last edited by madbadgalaxyman; 25-02-2013 at 02:35 PM.
The best source of (southern) galaxy diameters to very faint isophotes is the “Surface Photometry Catalogue of The ESO-Uppsala Galaxies”(1989) by Lauberts and Valentijn , which is also known as the ESOLV (or the ESO-LV).
Hello, Dana,
and Greg and Malc, and others who have commented about the large separation of the supernova from the host galaxy.
In practical terms, galaxies, when imaged to very very faint isophotes, are normally much larger in diameter than the diameter that is usually seen in amateur images, and galaxies are typically much larger in diameter even than the standard D25 diameter (to 25th Blue magnitude per square arcsecond) which is given for each galaxy in the galaxy catalogues.
(( The exact outermost Radial profile of surface brightness, as a galaxy's surface-brightness decreases with progressively increasing galactocentric radius, can have several different and well-defined forms. Some galaxies have a fairly sharp cutoff in light at some diameter, while other galaxies keep on extending outwards into the field .... even beyond 28th Blue Magnitude per square arsecond)
The best source of (southern) galaxy diameters to very faint isophotes is the “Surface Photometry Catalogue of The ESO-Uppsala Galaxies”(1989) by Lauberts and Valentijn , which is also known as the ESOLV (or the ESO-LV).
This very important catalog of bright galaxies is available in electronic form, and also (perhaps!) still in a paper version from the ESO.
Like the RC3, the ESO-LV is a large and homogeneous dataset, with relatively consistent and relatively high accuracy. The ESOLV is as important for southern galaxies as the Third Reference Catalogue of Bright Galaxies (=RC3) is for the all-sky bright galaxy population.
The ESO-LV gives the following angular diameters for the Major Axis (long axis) of NGC 5643:
Standard Diameter to 25th Blue magn. per sq. arcsec : :
305 seconds of arc (= 5.08 minutes)
Diameter to 26th Blue magn. per sq. arcsec : :
380 seconds of arc (6.33 minutes of arc)
Unfortunately, the ESO-LV doesn't give a diameter for this galaxy to the even fainter level of 27th Blue magnitude per square arcsecond, but the conclusion seems quite firm that a supernova which is 196 arcseconds (3.26 arcminutes) from the centre of NGC 5643 is still plausibly within the confines of this galaxy.
Now I would be as excited as the next man (or woman) if the supernova turns out to be associated with a dwarf companion of NGC 5643, but this numerical argument puts the conservative view that the supernova does belong to the big galaxy.
Here is the DSS image taken from wikisky.org, which shows the host galaxy extending outwards a lot further than it does in the other images in this thread;
(this is far from being the sharpest version of Digitized Sky Surveys, but it shows the galaxies at higher contrast than the other versions!)
Best Regards,
from
Bad Galaxy Man
P.S.
How accurate are ESOLV diameters of galaxies? They are usually about right, but occasionally they are very wrong!!
If anything, the galaxy diameters in the RC3 are even worse, as they are simply derived from an extrapolation of the inner (radial) light profile. At least ESOLV galaxy diameters are actual measurements, rather than extrapolations, or averages of several bad data-points. Still, even ESOLV is better for statistical (large number of galaxies) work than for finding a really accurate measurement.
The only way to get a really accurate angular diameter is to do CCD surface photometry of a galaxy.
Looking at the image above and comparing it with the discovery image, is there a possibility that the progenitor is in that pic
There is a triangle of stars in the position of the Supernova .
Cheers
I'm a complete newbie to estimating variables, and I'm way off with 11.8 compared to your 11.3 for around the same time. Were you using the AAVSO chart? If so, which comp stars did you use?
Thanks,
Malc
Hi Malc
The AAVSO updated the original chart a few days ago and some of the comparision stars around 11th magnitude were the ones that changed. If you downloaded the chart a while ago, it may pay to download it again. There is a 11.1, 11.4 and 11.6 mag comparision stars on the latest chart which is what I have been using.
A bit tangential to this discussion proper but interesting in its own right, I count 18 faint galaxy-like smudges in a 7' circle around TYC 7818-2402-1 roughly 7.5' SSE (14h 32m 17.5s / -44° 19' 48.7") from 5643's core. Even discounting 20% for FEAR (false expectations appearing real) methinks there might be a small cluster out there.
Does anyone know the deepest isophote level of the Wikisky images?
Back to 2013aa and N5643, any thoughts on the ejectee hypothesis based on the z value and radial vel. of nearby PGC 538542? This gx looks to be in the vm 21-22 range but doesn't turn up on Vizier, though it does on NED.
Dana,
I do agree with you, that the small galaxy that you mention is likely to be part of the same bound Galaxy Group as NGC 5643. It is much less likely that this is a galaxy at a different distance which has a "peculiar" (non-cosmological) velocity.
[[ As we all know well, actual observed galaxy recession velocities, are in practicenot actually proportional to galaxy distances, and a galaxy distance which is derived from a recession velocity could be greatly in error because of a large non-cosmological "individual" velocity of the galaxy. ]]
In general, outside of galaxy clusters, the local Hubble Flow within 2000 km/s seems to be very quiet. (the velocity-distance graph has few galaxies which are outliers). Aside from the Virgo and Fornax Clusters and the highly obscured Puppis Cluster of Galaxies, there are no large gravitational potentials within 2000km/s to move galaxies around with significant non-cosmological velocities.
Within 2000km/s redshift, I have found from long experience that (as we would expect!) the recession velocity of a galaxy is a good guide to (though not a measurement of!) a galaxy's actual physical distance, but there have been a very small number of individual cases where the velocity distance of a galaxy is very different from the actual as measuredphysical distance of that galaxy (obviously, because of the large individual velocity of the galaxy.)
My preferred tool for the initial investigation of the environment of a galaxy (galaxy clustering , and galaxy redshifts) and of adjoining regions of sky that are near to a galaxy, is the software starchart called "Guide 9.0" from www.projectpluto.com :
- it is quick (you can move from field to field, and zoom, very quickly)
- you can click on galaxy after galaxy to bring up redshifts (and other quantitative data) quickly
- it is data rich; it displays >100,000 galaxies, and the "popup" information for each galaxy is very extensive.
- it is highly configurable - virtually any Galaxy Catalog or Deep Sky Object catalog can be quickly loaded into "Guide" so that all the objects in the catalog are displayed on the electronic star chart
(for instance, my "Guide" software is configured to display all of the objects in: several catalogs of AGNs, the Virgo Cluster Catalog, and two different catalogs of the Fornax Cluster galaxies!)
- very high positional accuracy
- the Deep Sky Object and Galaxy data is loaded straight from the object catalogs; I have therefore found that the quantitative data about galaxies is reliable
- "Guide" is a lot faster and more convenient than DSS or Wikisky if the goal is quick movement from galaxy to galaxy, and a quick appraisal of each galaxy and its environment
cheers,
Robert
Last edited by madbadgalaxyman; 26-02-2013 at 02:35 PM.
Then put "SN 2013aa" in the search box, to find the observations.
Hello there, Andrew (Pearce),
I am currently fixated on trying to derive an estimated peak luminosity for the supernova; using its distance, its apparent magnitude, plus an estimate of the foreground extinction from our own Milky Way's dust screen. Currently doing a literature search to see if I can find something better than a distance derived from the galaxy's recession velocity! (because velocity distances can easily have errors of 20 percent, for galaxies which are at a recession velocity of ~1000 km/s)
Would you, or your fellow "variable star fanatics", like to have a go at deriving a reliable peak magnitude for the supernova, from the multitude of existing observations of this SN? [I am not familiar with the real (as against the "in my own mind") error budgets of the various observers]
I myself will have a try at getting some sense out of these 70 magnitude estimates, some of which are obviously very inaccurate.
Some of the errors given are absolutely ridiculous e.g. +/- 0.005 magnitude, which would be good going for the Hubble Space Telescope!
Also, looking at the large divergence between the various visual estimates of the supernova magnitude, I think my comment about some observers being easily half a magnitude out, are correct!! No sense in trying to make an average, or even a weighted average, of bad data points!!
cheers,
Robert
Last edited by madbadgalaxyman; 26-02-2013 at 05:57 PM.
Welcome to the world of variable star observing! As you can see it can be quite a difficult thing to sort through observations and make sense of them in trying to determine the "signal" and the "noise" component. There is a very good book by Grant Foster, "Analyzing Light Curves - A Practical Guide" which gives various statistical methods that are commonly used by the AAVSO when analysing light curves which contain various degrees of scatter. I think it's fair to say that the CCD observations of SN 2013aa by only a handful of observers show less scatter than the visual observers and looking at the light curve, they seem to show a clear peak magnitude of 11.6 around Feb 20-22.
However from a visual perspective, the SN has definitely appeared slightly brighter than 11.6 and this can be relatively easy to judge as there is a nearby comparison star of 11.6 and I personnally have seen the SN brighter than this star. My own obervations indicate a peak brightness of 11.3. But as you can see from the light curve there have been visual estimates up to 11.0. I can't explain exactly why there has been a difference between the CCD V and visual observations.
A scatter of 0.5 mag amongst a bunch of visual observers is not uncommon. Also I'm not sure how much of an effect the fact that the AAVSO changed some of the comparision star magnitudes on the chart a short while ago has had and whether all of the visual observers were using these corrected magnitudes as this could affect the observations up to 0.2 mag or so.
Sorry for not really giving a definitive answer, but I feel the peak was somewhere between 11.3-11.6.
Hi Robert
Welcome to the world of variable star observing! As you can see it can be quite a difficult thing to sort through observations (.......)
(......)the CCD observations of the SN by only a handful of observers show less scatter than the visual observers and looking at the light curve, they seem to show a clear peak magnitude of 11.6 (....)
(........)However from a visual perspective, the SN has definitely appeared slightly brighter than 11.6 and this can be relatively easy to judge as there is a nearby comparison star of 11.6 and I personally have seen the SN brighter than this star. My own observations indicate a peak brightness of 11.3.(......)
(.....)I feel the peak was somewhere between 11.3-11.6.
Andrew,
Pity that I don't have the statistical tools you mention, in my 'mental toolkit', so as to sort out that messy magn. data.
But I do know (from experience) a lot about the errors made in visual observations, by means of the "wishful" thinking of the eye-brain system. Given that a 10 or 20 percent difference in apparent brightness is hard for the eye to spot, an observer's attitude (bias)(his preconceptions about object brightness) could well influence whether or not a star seems brighter, or the same brightness, or fainter, than a comparison star;
I think, at the level of 0.1 to 0.3 magnitude, a perceptual bias could easily creep in and distort the observer's visual magnitude estimate for a variable star.
Unfortunately, an error of 0.3 magnitudes in the apparent magnitude of the Supernova is large, when we wish to use it for the purposes of estimating the luminosity (absolute magnitude)(absolute brightness) of this astronomical object. The distance error for an individual galaxy can easily amount to 20 percent , which equates to an additional error of 0.4 magnitudes in the derived luminosity of the supernova.
Galaxyman's question to Mr "Variable" Pearce:
Do your visual (that is, made using the "eye+brain system") magnitude estimates need to be mathematically transformed into the Johnson V-band Magnitudes for the purpose of making a really accurate comparison with V-band measurements made using photoelectric and CCD photometry??
Some of my textbooks state the following:
(1) The Johnson photometric V-band filter was actually chosen so as to approximate the visual response (the band-pass) of the eye (the eye's response curve). That is, the filter's transmission curve has a peak filter transmission (maximum brightness) near 550nm and a Transmission Curve width ( Full-Width-at-Half-Maximum) of about 90nm.
(2) The bandpass and sensitivity curve of the eye is, however, different from that of the standard photometric V filter, being composed of a complex mix of responses from the rods and from three different types of cones.
(e.g. the well-known shift of about 50nm in the peak sensitivity between the rods and the cones)
Therefore, do visually-estimated magnitudes (visual magnitudes) need to be mathematically transformed into V-band Johnson-Cousins magnitudes, if they are to be accurately compared with V-band magnitudes?
Congratulations Stu and to the rest of the BOSS team- what an extra fantastic discovery re it being such a bright one.
I'm so excited that I finally get to observe one from you guys!
Sorry about the late response, I've been posting this news all over the place on facebook but I forgot to come back here to the source (I'm normally pretty quick to applaud you guys) ... so embarrassed!
It seems to be raining forever here in South east Queensland grrrr .
As mentioned in a previous post, the perception that this supernova is "a long way out from NGC 5643" is essentially a perception created by the limited sensitivity of our observations.
For instance, the surface photometry of this galaxy in the Carnegie-Irvine Galaxy Survey gives a galaxy diameter, corrected for inclination and the effects of extinction, of 6.82 arcminutes, measured out to the 26.5 B magnitude per square arcsecond Isophote (this is a very-very-low level of surface brightness)
( Carnegie-Irvine Galaxy Survey: http://cgs.obs.carnegiescience.edu/CGS )
Data associated with the paper Pierce & Tully, 2000, ApJ, 533, 744, and published in http://edd.ifa.hawaii.edu ,'
gives an observed (uncorrected) radius, out to the same low level of surface-brightness, of 3 minutes and 23 arcseconds, for NGC 5643.
I can still remember "way back when" in 1991, when just about all of the data that you could find about a specific galaxy was found in two or three Galaxy Catalogs and two or three Atlases of Galaxies, which you mostly looked up in the paper (physical) version of the catalog or atlas. There was also a lot of other "hidden" data about a galaxy, but it was not accessible, as it was stashed away in observatory archives all over the planet.
As is, I just spent 6 hours on the internet, looking at numerical data about NGC 5643, and I still haven't looked at all of the available data!
Galaxyman's question to Mr "Variable" Pearce:
Do your visual (that is, made using the "eye+brain system") magnitude estimates need to be mathematically transformed into the Johnson V-band Magnitudes for the purpose of making a really accurate comparison with V-band measurements made using photoelectric and CCD photometry??
[U]
cheers,
madbadgalaxyman
Hi Robert
As with most things, it's not straightforward! The relationship between the visual magnitude a visual observer sees and a Johnson V mag does depend on the individual observer! Obviously this is far from ideal. However about 14 years ago, the AAVSO performed a study to try and quantify this relationship amongst a whole bunch of observers. An excellent paper was written by R.H Stanton entitled "Visual Magnitudes and the 'Average Observer':The SS Cygni Field Experiment" which was published in the Journal of the AAVSO back in 1999. It is freely available on the web if you do a Google search you'll find it. The average correction between visual and V magnitudes was found to be:
visual mag = V + 0.210 x (B-V)
I haven't applied this to the estimates of SN 2013aa as I haven't checked whether there have been an B mag estimates made.
The article also goes on to note that "random errors on the order of 0.2 magnitude can be expected when data from many observers are combined".
As with most things, it's not straightforward! The relationship between the vis. magnitude a visual observer sees & Johnson V mag does depend on the individual observer!(.....)
(......)An excellent paper was written by R.H Stanton entitled "Visual Magnitudes and the 'Average Observer':The SS Cygni Field Experiment"
in the Journal of the AAVSO back in 1999.
(.....)The average correction between visual and V magnitudes was found to be:
visual mag = V + 0.210 x (B-V)
(.......) "random errors on the order of 0.2 magnitude can be expected when data from many observers are combined".
Thanks for that, Andrew.
Your useful answer saves me a lot of time , as I am fully occupied ("up to my neck") in large quantities of data about NGC 5643!
The combined error of 0.2 sounds about right for the AAVSO observers' visual data about the apparent magn. of 2013aa, as long as one ignores statistical outliers among the scatter of data points...... for instance. there is a cluster of visual observations near 11.1 to 11.2 visual magn. which I think should be ignored in calculating a mean magnitude of the SN. Perhaps these observations are the result of the sort of "wishful thinking" and "cognitive-perceptual bias" that I mentioned; these observers perhaps wanted the SN to be closer to magn. 11
While I am not particularly statistically savvy, I do look at a lot of numerical galaxy data, both the good and the bad and the ugly, so I have a good feel for the sort of bad data points that should be rejected in an analysis.
Perhaps AAVSO should be less "democratic" and only accept estimates from the most accurate visual observers!! It is, after all, possible to measure the average error of a specific observer.
cheers, Robert
"Science is not about democracy, or about sympathy for the underdog or for the weaker workers. It is about getting the best and most hard-working people to throw 'everything they've got' at a difficult problem"
- madbadgalaxyman
As most people know, the weather has been very crappy for the last 3 weeks. This has stopped me getting any follow up spectra of this SN.
On 5/3/13 I had a partly clear evening but with 20-30kt winds to make it difficult.
I achieved about 15 min of exposure only and even then the star was jumping all around the slit so only about 1/2 of the time was anything being registered. Despite this I obtained a noisy spectra. It shows some progression of the shape of the spectra.
See http://users.northnet.com.au/~bohlse.../sn_2013aa.htm
.
