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RW Cephei great dimming

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#26 robin_astro

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Posted 16 December 2022 - 06:10 AM

 

 

The D lines are broad and although saturated show significant structure. Doesn't this imply an interstellar origin ?

 

I mean a significant IS contribution. There will also be a stellar component of course. 

 

 

Robin



#27 VY Canis Majoris

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Posted 17 December 2022 - 05:13 AM

Here is the complete light curve from AAVSO with a plotted mean using 1000-day bins. It is clear that the average magnitude has steadily increased since 1950. I'm sure this must have some implication for the nature of this recent great dimming.

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  • RW Cep LC.PNG

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#28 flt158

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Posted 17 December 2022 - 07:45 AM

As some of you know, I have a copy of Robert Burnham's Celestial Handbook. 

It is stated in this marvellous book on page 578 that RW Cephei can vary in magnitude from a maximum of +7.6 to somewhere below magnitude +9. 

How faint the star can become is not made clear in Burnham's book. 

But isn't that 7.6 magnitude rather odd?

Looking at the above light curve, RW Cephei can be as bright as +6.8. 

To me personally the star is very strange. 

Could Burnham's astronomers gotten it wrong?

 

By the way, Burnham gives the star's spectrum as M0. 

I would also encourage those here who have spectroscopes to try and figure out the star's current spectral class.  

 

My weather here in Ireland is not helping matters, i.e. it is too changeable. 

I should have clear skies next Wednesday night. 

I wonder what colour RW Cephei will be. 

 

Best regards from Aubrey. 



#29 VY Canis Majoris

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Posted 17 December 2022 - 07:55 AM

As some of you know, I have a copy of Robert Burnham's Celestial Handbook. 

It is stated in this marvellous book on page 578 that RW Cephei can vary in magnitude from a maximum of +7.6 to somewhere below magnitude +9. 

How faint the star can become is not made clear in Burnham's book. 

But isn't that 7.6 magnitude rather odd?

Looking at the above light curve, RW Cephei can be as bright as +6.8. 

To me personally the star is very strange. 

Could Burnham's astronomers gotten it wrong?

Maybe they confused the star with RW Cygni, which has a very similar magnitude range to the mentioned 7.6-9.0?


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#30 yuzameh

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Posted 17 December 2022 - 08:59 AM


The D lines are broad and although saturated show significant structure. Doesn't this imply an interstellar origin ?

I see what you're saying, differing zones of differing kinematics at differing distances between us and the star.  Not sure how clumpiness in circumstellar matter adds in for NaI D though, especially as any surrounding material will itself be layed due to resulting from many different outbursts over time.

 

Interstellar fits best as simple answer that's not trying to read too much into it.  On the other hand, once I learnt how to download these ELODIE data using TopCat SSAP and SPLAT-VO indirectly and directly respectively I found there were just over half a dozen of them and overlaying the rest wavelengths of the sodium doublet it was obvious that the absorption varied in radial velocity over time, although it did keep its overall morphology.  I do hope some of the bigger scopes are taking some higher resolution stuff.

 

Not so cold, in fact positively warm, for the next little while, which of course means cloud, during the dark of the moon part of the month again, so you will probably be stymied for any further local imaging.



#31 yuzameh

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Posted 17 December 2022 - 09:07 AM

As some of you know, I have a copy of Robert Burnham's Celestial Handbook. 

It is stated in this marvellous book on page 578 that RW Cephei can vary in magnitude from a maximum of +7.6 to somewhere below magnitude +9. 

How faint the star can become is not made clear in Burnham's book. 

But isn't that 7.6 magnitude rather odd?

Looking at the above light curve, RW Cephei can be as bright as +6.8. 

To me personally the star is very strange. 

Could Burnham's astronomers gotten it wrong?

 

By the way, Burnham gives the star's spectrum as M0. 

I would also encourage those here who have spectroscopes to try and figure out the star's current spectral class.  

 

My weather here in Ireland is not helping matters, i.e. it is too changeable. 

I should have clear skies next Wednesday night. 

I wonder what colour RW Cephei will be. 

 

Best regards from Aubrey. 

This one is a simple one.  He'll be quoting photographic magnitudes, which with normal photographic plates meant a blue bias in sensitivity.  He'll likely have picked his variable star data from the 4th edition of the General Catalogue of Variable Stars, GCVS.  I think someone earlier in the thread noted that a lot of the older references give the photographic range.

 

I could loosely say think of visual as greeny-yellow, think of old astronomical glass plates as bluish, so compared to red magnitudes, visual is fainter and photographic plates fainter still.  You can get a hint of this from the following panstarrs link, even though the object is seriously over-exposed.

 

g is kind of just bluish of visual to bluish, r is reddish, and i includes just a bit of the visual but is mostly redward of the red bit of the rainbow, the next "colour" along if you will, that is if we could see it.  Note the differences.  Ignore the colour composite and the y and z band images.

 

http://ps1images.sts...500000&catlist=


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#32 yuzameh

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Posted 17 December 2022 - 09:25 AM

Here is the complete light curve from AAVSO with a plotted mean using 1000-day bins. It is clear that the average magnitude has steadily increased since 1950. I'm sure this must have some implication for the nature of this recent great dimming.

I dunno, I prefer not to use AAVSO visual data for objects like this, they've, or at least they didn't have, no real means of reformulating older measures if a sequence changed, and they've lumped in data from just about every other group's archives with different groups using different techniques, and you're having to use a moving average to show it but the scatter/noise on this data is way bigger than the signal.

 

It's often better to get a regional group's data, with just a few long term observers involved.

 

Search for the BAA (British AA) photometric database, which gives a curve that looks more flat, although there does seem to be an abrupt jump in brightness at one point (abrupt temporally, the mean magnitude shift is quiet small).  AFOEV (France and Europe) data can be found here, it's all hidden away in the CSD Strasbourg ftp servers ftp://cdsarc.cds.unistra.fr/pub/afoev/cep/rw , VSOLJ (Japan) http://www.kusastro....SOLJ/index.html , and their used to be the HAA (Hungary), not sure where that's stored nowadays.  The Southern Hemisphere stuff is logged by the RASNZ (New Zealand), but I don't think that was ever directly available online, though some of their observers would also send their data along to both BAAVSS and/or AAVSO.

 

I've always had a bit of a liking for the AFOEV stuff, there's data for a wider number of objects than exists in the BAAVSS data, but both have good long term coverage but with a tendency for big gaps between WWI and WWII.

 

EDIT : I've just been doing a news catchup around the websites and noticed this https://www.aavso.or...lert-notice-804 where AAVSO are requesting photometric and spectroscopic campaigns.  It metions a 2002 brightening of mean magnitude with a 2021 return to the old ways.  This can be kind of familiar in post AGB stars and YSOs and other stars with circumstellar matter, analogous to when the Sun pokes through the clouds for a short while, or conversely during some faint phases when the clouds thicken at some point and the day gets dimmer.  I think there's some sort viewpoint nowadays that something so simple actually explains the so called Changing Line AGN galaxies too.  Such short timespan of occurrence events can also occur because of sequence changes so you tend to need the metadata of the observational archives to ensure there are no reasons due to a methodological change for that time period. 


Edited by yuzameh, 17 December 2022 - 09:41 AM.


#33 robin_astro

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Posted 17 December 2022 - 09:49 AM

 

By the way, Burnham gives the star's spectrum as M0. 

I would also encourage those here who have spectroscopes to try and figure out the star's current spectral class.  

 

 

Looking more closely at my spectrum from 2022-12-12, I estimate currently K4i with E(B-V) =0.65. Here it is overlaid on the Pickles K4i spectrum. 

 

RWCep_20221212_THO_best_match.png

 

The TiO bands are significantly weaker than in M stars, here overlaid on M0iii (There is no M0i in the Pickles library. I would need to hunt a standard down)

 

RWCep_20221212_THO_M0_poor_match.png

 

Cheers

Robin


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#34 robin_astro

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Posted 17 December 2022 - 09:58 AM

  I do hope some of the bigger scopes are taking some higher resolution stuff.

 

Not so cold, in fact positively warm, for the next little while, which of course means cloud, during the dark of the moon part of the month again, so you will probably be stymied for any further local imaging.

 

 At this magnitude R 10-20k is possible at reasonable SNR even with modest apertures, though with my equipment only over a narrow wavelength range per observation. (I will put the word out among some echelle owners). The run of clear nights has indeed come to an end here though. .

 

 

Cheers

Robin


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#35 mwr

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Posted 17 December 2022 - 11:13 AM

 

 

The TiO bands are significantly weaker than in M stars, here overlaid on M0iii (There is no M0i in the Pickles library. I would need to hunt a standard down)

 

 

The clear presence of TiO bands is quite interesting if one takes a look into a paper that was published in 2003:

 

"The spectral type of RW Cep is uncertain, this star being referenced as a
G8, K0 or M0 supergiant. Its spectrum does not contain TiO bands and
we estimate Teff  5300 K from V−K. A G-type supergiant seems thus
more plausible." 

https://www.research...Supergiants.pdf

 

The V magnitude reported in this paper for RW Cep was 6.67 mag.

 

It is tempting to speculate that the dimming of RW Cep is accompanied by cooling of its photosphere with concomitant formation of TiO molecules. The match of Robin's fine spectrum with a K4 I standard spectrum is striking and would so far be the coolest spectral class reported for this star (about 4000 K effective surface temperature if I take the data from "Allen's Astrophysical Quantities" for the MK spectral classes; Chapter 15.3.1 Table 15.7: Calibration of MK Spectral Types).


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#36 robin_astro

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Posted 17 December 2022 - 11:23 AM

 once I learnt how to download these ELODIE data using TopCat SSAP and SPLAT-VO indirectly and directly respectively I found there were just over half a dozen of them and overlaying the rest wavelengths of the sodium doublet it was obvious that the absorption varied in radial velocity over time, although it did keep its overall morphology. 

I would be interested to see those additional spectra are they easily accessible?  Not sure I understand the RV variations (I presume they are heliocentric corrected).The star will have a strong photospheric Na D component. Are you saying that the complex line profile  is varying in RV as a whole?  On what sort of timescale?  Pulsations or binary might do this but the circumstellar/interstellar material moving in step would be surprising. 

 

Cheers

Robin



#37 flt158

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Posted 17 December 2022 - 02:14 PM

Thank you, Robin, for your reply. 

I believe you have nailed it. 

K4i it is. 

I don't understand every statement here, but I'm content with this spectral reading. 

I must also thank VY Canis Majoris, mwr, yuzameh and others for all their contributions. 

 

I have observed some K4 stars, and I'm looking forward to finding this one.

 

Clear skies from Aubrey.   



#38 robin_astro

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Posted 17 December 2022 - 03:24 PM

 

It is tempting to speculate that the dimming of RW Cep is accompanied by cooling of its photosphere with concomitant formation of TiO molecules.

I am not sure that the presence of TiO in the spectrum is restricted to  the current dimming. The classical region used for spectral classification is at the blue end of the spectrum but  if we look further to the red end where the TiO band are more obvious, specifically at the broad absorption attributed to TiO around 6250A we find that, despite the apparent differences in the continuum shape, there is evidence of it at similar intensity in the all spectra we have (mine, the two in the AAVSO database and  one in the ELODIE archive)

 

rwcep_6250.png

 

This feature only appears in stars K2i and cooler in the Pickles reference spectra

 

pickles_6250.png

 

Cheers

Robin


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#39 VY Canis Majoris

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Posted 17 December 2022 - 04:19 PM

Something interesting I'd just like to share, is that according to one source the spectrum can go as early as F0Ia during some phases, losing its hypergiant luminosity class in the process.

 

https://ui.adsabs.ha.....145D/abstract

 

This seems to be the only source stating this so there hasn't been any independent confirmation.



#40 yuzameh

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Posted 18 December 2022 - 12:35 AM

I would be interested to see those additional spectra are they easily accessible?  Not sure I understand the RV variations (I presume they are heliocentric corrected).The star will have a strong photospheric Na D component. Are you saying that the complex line profile  is varying in RV as a whole?  On what sort of timescale?  Pulsations or binary might do this but the circumstellar/interstellar material moving in step would be surprising. 

 

Cheers

Robin

I haven't looked at the images since the other day so I'm going from memory, and I'm at the bottom of the learning hill on spectral data so I won't be embarrassed if I've made any gaffs in understanding, but the morphology/profile looks the same in NaI D, but when the elodie data from different years are loaded they drift in position relative to the at rest wavelength for NaI D as plotted from the splat-vo line references.  Each one of the doublets looks very much like the other, and each are tripled in that at the trough base they all have lower intensity gaps but nowhere near all the way back up to the continuum, these could be an artefact for all I know but some of the other lines don't do the same thing.  I looked at four at random, including the most recent one.  I did read somewhere that the radial velocity was variable as well, but then again it is a pulsator.

 

Now, using the SSAP server in TopCat, the euro vo registry (only one that works for spectra) and searching on the keyword elodie and searching on coordinates resolved from object RW Cep via sesame using a 12 arcsec search radius there appear to be 22 spectra available.  I'll cut and paste them below, beware wordwrap errors.  Their MJD are logged, plus other data.

 

Now, each one includes a link and I found by simply trying it that if I cut and pasted one of those links directly into a browser url bar a save dialogue popped up asking me where I wanted to download the fits file.  These imported into both TopCat and splat-vo easily enough, and I also experimented with using the SSAP server in splat-vo to get them as well.  There used to be a better spectrum viewer in java at hearsarc years ago but it seems to have disappeared, it had far more reference lines (possibly too many) from a large general (not astronomy biased) atomic line reference.

 

Anyway, here they are, I had to use splat as they are some 1d format type thing that gives 2d graphs as splines according to the fits.

 

objname          access_reference                                                                                     j2000                 dataidtitle             mjd   exptime snr   instrume redshift              spectralaxisname spectralaxisunit
  BD+551572        " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:19990820/0020   " "(335.77923, 55.96328)" Elodie/BD+551572        51411 3505.41 287.8 Elodie   -0.000190911589011575 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030529/0010   " "(335.77923, 55.96328)" Elodie/HD212466         52789 1800.46 210.4 Elodie   0                     WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030704/0019   " "(335.77923, 55.96328)" Elodie/HD212466         52825 705.24  108.9 Elodie   -0.000183119687693657 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030704/0018   " "(335.77923, 55.96328)" Elodie/HD212466         52825 1800.46 178.2 Elodie   -0.000180377845705931 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030705/0022   " "(335.77923, 55.96328)" Elodie/HD212466         52826 600.12  121.0 Elodie   -0.000182956244558136 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030820/0017   " "(335.77923, 55.96328)" Elodie/HD212466         52872 1800.45 196.8 Elodie   -0.000188459941978754 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030820/0021   " "(335.77923, 55.96328)" Elodie/HD212466         52872 600.39  115.1 Elodie   -0.000188543331333612 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030916/0013   " "(335.77923, 55.96328)" Elodie/HD212466         52899 1200.4  258.4 Elodie   -0.000187626048430176 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030916/0015   " "(335.77923, 55.96328)" Elodie/HD212466         52899 300.28  135.3 Elodie   -0.000187599363836621 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20030916/0014   " "(335.77923, 55.96328)" Elodie/HD212466         52899 300.28  133.3 Elodie   -0.00018760603498501  WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040114/0026   " "(335.77923, 55.96328)" Elodie/HD212466         53019 600.17  53.7  Elodie   -0.000195958312767573 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040114/0024   " "(335.77923, 55.96328)" Elodie/HD212466         53019 600.33  92.5  Elodie   ""                    WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040114/0025   " "(335.77923, 55.96328)" Elodie/HD212466         53019 600.33  60.7  Elodie   -0.000196091735735345 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040214/0009   " "(335.77923, 55.96328)" Elodie/HD212466         53050 1200.4  72.8  Elodie   -0.000197462656729208 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040214/0010   " "(335.77923, 55.96328)" Elodie/HD212466         53050 1800.51 48.6  Elodie   -0.000197459321155014 WAVE             nm             
  J221719.0+555721 " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040427/0027   " "(335.77923, 55.96328)" Elodie/J221719.0+555721 53123 900.34  140.2 Elodie   0                     WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040521/0029   " "(335.77923, 55.96328)" Elodie/HD212466         53147 3000.63 218.9 Elodie   -0.000195598070754587 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040623/0032   " "(335.77923, 55.96328)" Elodie/HD212466         53180 1200.45 126.9 Elodie   -0.000191231804134229 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040724/0023   " "(335.77923, 55.96328)" Elodie/HD212466         53211 1800.46 106.7 Elodie   -0.000187002296055839 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040724/0022   " "(335.77923, 55.96328)" Elodie/HD212466         53211 602.31  65.5  Elodie   -0.000187025645075199 WAVE             nm             
  HD212466         " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20040824/0045   " "(335.77923, 55.96328)" Elodie/HD212466         53242 1800.46 68.1  Elodie   -0.000183009613745245 WAVE             nm             
  RW_CEP           " http://atlas.obs-hp....tion/fits&z=s1d|tbl&o=elodie:20050202/0006   " "(335.77923, 55.96328)" Elodie/RW_CEP           53404 1200.56 61.8  Elodie   -0.000177279097279413 WAVE             nm

 

As I say, if you just use one of these links at random, eg

 

http://atlas.obs-hp....e:20040623/0032

 

it'll cough up a fits file.

 

It seems they are from 2003 to 2005 with all bar two during 2004.  I made an attempt at showing the 2003 and 2005 one along with the Na I D rest reference line, but I haven't read any full fits headers to see whether they are geocentric or helioscentric.

 

 

as an afterthought here's the Halpha from the self same plot as the Na I D using the self same data.

 

 


Edited by yuzameh, 18 December 2022 - 12:45 AM.

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#41 yuzameh

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Posted 18 December 2022 - 01:07 AM

Let's go the whole hog.  Here's the only other stuff I found from something called "polarbase ssap".

 

Again, just copy and paste the links into a browser.  However, with FITS being the standard it isn't some programs won't read these .fts files, so I had to import them into TopCat and then export them as .FITS files before splat recognised them, although TopCat read the .fts file columns alright.  They still have plotting glitches with some straight lines joining different points

 

spectralsi FluxAxisName FluxAxisUnit  fluxsi url                                                                       format           SpatialLocation    SpatialExtent TimeLocation       SpectralLocation SpectralExtent
  espadons_2006_012_882261i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882261i_u.fts application/fits "(335.779, 55.9632)" 1.6           54077.27988425926  708.0            678.0        
  espadons_2006_012_882261p_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882261p_u.fts application/fits "(335.779, 55.9632)" 1.6           54077.28251157407  708.0            678.0        
  espadons_2006_012_882262i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882262i_u.fts application/fits "(335.779, 55.9632)" 1.6           54077.28158564815  708.0            678.0        
  espadons_2006_012_882263i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882263i_u.fts application/fits "(335.779, 55.9632)" 1.6           54077.28337962963  708.0            678.0        
  espadons_2006_012_882264i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882264i_u.fts application/fits "(335.779, 55.9632)" 1.6           54077.28517361111  708.0            678.0        
  espadons_2006_012_882261i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54077.27988425926  708.0            678.0        
  espadons_2006_012_882261p   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54077.28251157407  708.0            678.0        
  espadons_2006_012_882262i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54077.28158564815  708.0            678.0        
  espadons_2006_012_882263i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54077.28337962963  708.0            678.0        
  espadons_2006_012_882264i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54077.28517361111  708.0            678.0        
  espadons_2006_012_882435i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.irap.omp.eu/downloadFits/espadons/2006/012/882435i_u.fts application/fits "(335.779, 55.9632)" 1.6           54078.20097222222  708.0            678.0        
  espadons_2006_012_882435p_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882435p_u.fts application/fits "(335.779, 55.9632)" 1.6           54078.20527777778  708.0            678.0        
  espadons_2006_012_882436i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882436i_u.fts application/fits "(335.779, 55.9632)" 1.6           54078.20384259259  708.0            678.0        
  espadons_2006_012_882437i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882437i_u.fts application/fits "(335.779, 55.9632)" 1.6           54078.206712962965 708.0            678.0        
  espadons_2006_012_882438i_u 213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX         dimensionless 1      http://polarbase.ira...2/882438i_u.fts application/fits "(335.779, 55.9632)" 1.6           54078.20958333334  708.0            678.0        
  espadons_2006_012_882435i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54078.20097222222  708.0            678.0        
  espadons_2006_012_882435p   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54078.20527777778  708.0            678.0        
  espadons_2006_012_882436i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54078.20384259259  708.0            678.0        
  espadons_2006_012_882437i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54078.206712962965 708.0            678.0        
  espadons_2006_012_882438i   213722     "(335.779, 55.9632)" AWAV             nanometer        "1E-9 L"   FLUX_NOR     dimensionless 1      application/fits "(335.779, 55.9632)" 1.6           54078.20958333334  708.0            678.0

 

All of these seem to be on the same night.

 

 

 


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#42 VY Canis Majoris

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Posted 18 December 2022 - 02:16 AM

The recent measured B-V index seems strange, the value is 2.059, which actually seems even hotter than the star usually appears. Both dust and a minima in the pulsation would cause a cooler observed B-V index.

 

Dereddening it assuming E(B-V) = 0.65 does however give a color consistent with a K3-4I star (following Allen's Astrophysical Quantities once again), a nice independent confirmation of the spectral type.


Edited by VY Canis Majoris, 18 December 2022 - 03:18 AM.

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#43 mwr

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Posted 18 December 2022 - 06:15 AM

Yesterday we had a clear cold night and I could do some imaging and differential tricolor green channel photometry on RW Cep:

 

(Edit: V-magnitude was corrected to 7.8 mag; wrong algorithm for debayering)

 

RW Cep is easily seen as a colorful orange star in a rich Milky Way field near the open cluster Berk 94 (https://www.cloudyni...ep#entry9934088)

 

However, getting a reliable spectrum with my slitless SA-200 grism setup was not possible due to the disturbing field stars in the rich Milky Way field:

 

 

A vertical stretch of  the spectrum shows a multitude of field stars in the spectral strip (the curse of slitless spectroscopy). However, in the near infrared an intense absorption line of the triplet of ionized Calcium (Ca II) was clearly visible. 

 


Edited by mwr, 18 December 2022 - 01:55 PM.

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#44 robin_astro

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Posted 18 December 2022 - 07:35 AM

 

 

As I say, if you just use one of these links at random, eg

 

http://atlas.obs-hp....e:20040623/0032

 

it'll cough up a fits file.

 

It seems they are from 2003 to 2005 with all bar two during 2004.  I made an attempt at showing the 2003 and 2005 one along with the Na I D rest reference line, but I haven't read any full fits headers to see whether they are geocentric or helioscentric.

 

 

Thanks !  Lots to look at there. I quickly overplotted your example (roughly filtered to match resolution) on my recent spectrum

 

RWCep_THO_20221212_ELODIE_2040624.png

 

(The fits header is agnostic on whether a heliocentric correction has been made)

 

Cheers

Robin


Edited by robin_astro, 18 December 2022 - 07:37 AM.


#45 robin_astro

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Posted 18 December 2022 - 09:53 AM

 I made an attempt at showing the 2003 and 2005 one along with the Na I D rest reference line, but I haven't read any full fits headers to see whether they are geocentric or helioscentric.

 

 

It seems the ELODIE spectra are "as measured" ie geocentric .I compared two of the spectra from 2004 taken several month apart which show a clear shift. The wavelength shift disappears after correcting to the heliocentric reference frame. (Note the sharp lines which were aligned originally have shifted. These are telluric lines from our atmosphere)

 

Cheers

Robin

 

RWCep_ELODIE_heliocentric.png



#46 pbealo

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Posted 18 December 2022 - 12:35 PM

AAVSO issued an Alert Nootice two days ago asking for RW CEP observations.

 

See:  https://www.aavso.or...lert-notice-804


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#47 yuzameh

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Posted 18 December 2022 - 02:28 PM

(The fits header is agnostic on whether a heliocentric correction has been made)

 

I suspected as much, but I wasn't sure if I just wasn't looking properly.

 

It looks like spectra fits files are even more problematic than photometry and image ones in terms of what can be automatically used by applications.  There is a means in splat to choose what-centric, but I'm not clear if you did a heliocentric correction manually by assessing the MJD and working out the values yourself or whether the fits file had some info in there to enable you to do so, say your application simply using ra, dec and MJD to correct to heliocentric, which if I remember correctly are the three bits of data needed at base.

 

That's why I never play with jupyter notebooks and python, I have enough trouble following what the data are as provided and figuring out how best to use them in user friendly multiplatform java apps without esoteric python which I'd have to learn to code in to tweak correctly and in the case of jupyter seem to be bespoke tailored to their authors' needs rather than widely applicable.

 

Know your data, then learn the software.



#48 yuzameh

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Posted 18 December 2022 - 02:47 PM

It seems the ELODIE spectra are "as measured" ie geocentric .I compared two of the spectra from 2004 taken several month apart which show a clear shift. The wavelength shift disappears after correcting to the heliocentric reference frame. (Note the sharp lines which were aligned originally have shifted. These are telluric lines from our atmosphere)

 

Cheers

Robin

 

attachicon.gifRWCep_ELODIE_heliocentric.png

Argh, cursewords!  Fair enough though, I've learned something, which is always useful.  Thanks for that.  I usually get annoyed when people make blind assumptions, but in this case I myself assumed geo and helio centric differences were negligible in terms of relative motion, but I seem to remember orbital velocity of the Earth is 30 km/s or such, so that's my fault.

 

This is informative though, I think you're saying that the atmospheric telluric lines are aligned when geocentric whilst the stellar ones aren't but on heliocentric correction the true stellar ones then align but the telluric atmospheric ones now become misaligned because being local lines (within 100 km or so) they were already naturally aligned in the first graph.

 

That's a usable simple diagnostic i can remember.  I know just need to know if splat takes the mjd etc to autocorrect when I swap the input to "sun centred".  Trouble is I think it default assumes heliocentric on "agnostic" data.

 

I'm assuming now that if there had been RV shifts it would have of far smaller difference.  Yep, I know there'll be a formula for that, something about the wavelength ratio, or possibly wavelength difference divided by heliocentric rest wavelength being equivalent to z=v/c, but at the moment I just want to get the qualitative feel for it all.

 

Cheers

 

Interesting star though.  Glad it's catching on.  I noticed when RS Oph was found on the rise there was quite some significant delay in the professionals and the non-optical satellites catching on.  Probably the same here, in fact I'm amazed it got mentioned on astronomerstelegram.org.  All a bit worrying for the upcoming T CrB event as I think the thing only lasts a day or two at brightest.  Needs the same response a gravity wave or neutrino burst would get.  Cosmology and "exoplanets" for the pros, some of us still love the stars though!



#49 yuzameh

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Posted 18 December 2022 - 04:28 PM

Before I completely forget, there were other sources of professional data which I had no luck with.  I found several on VizieR.  The best one was a DAO log (Dominion Astrophysical Observatory) which will give you two decades worth of data on RW Cep, sparsely spread.  I couldn't get the files to display in anything though, well, nothing meaningful, TopCat just showed a very narrow bandwidth with a peak which wasn't right.

 

https://vizier.cds.u...r&-oc.form=sexa

 

then press submit and click on datalink.  It worked the other day, but is giving a 503 server unavailable today.  A few of the ADC sites can be like this.  Maybe you'll have better luck.  Weekends can often be maintenance days.  That's on a 1.2m scope with the "McKellar Spectrograph".

 

VizieR based CADC logs (Canadian Astronomical Data Centre) also had some others, I think one was the 3.6m CFHT on Mauna Kea, but the datalinks there looked to be dead.  I myself have found the direct CADC difficult if not impossible to use since they "improved" it, but I tend not to update my browser every two seconds like we're supposed to so it could be that.  Here's the logs, but the VizieR outlinks don't seem to work anymore so you'll have to try the CADC direct.

 

http://vizier.cds.un..._r&-oc.form=deg new log.  Old log looks as though it might be radio, filter is CO 2-0 (rovibrational?) http://vizier.cds.un..._r&-oc.form=deg

 

If you don't use TopCat, try it.  It does lots of things you can freely ignore and if it doesn't all the plotting needed it is the best multiway data type converter going, and it has TAP and SSAP (simple spectral access protocol: SIAP is simple image access protocol, you can also get at that one via Aladin's collections).  I found the TopCat SSA protocol system the easiest way to get at the data holdings, and it wasn't until I used that that I realised their data files were logs with links to the fits files rather than the fits files which was why I wasn't able to autoplot them in VizieR.  Needs JAVA 1.8 minimum, I use a local install of the JRE version (there's an open Java now too) as .jnlp and JDK tend to try and take over the computer in my view, and I go out of my way to nobble the updater in autostart and services and task scheduler, as I need a basic stable environment that I know will work with the small number of astro java stuff I can find no alternative to. http://www.star.bris...uk/~mbt/topcat/

 

If a search doesn't work in SSA protocol in TopCat try the other registries, especially the euro vo, and it will also allow input of a bespoke repository url.

 

If you want to play in the UV then http://sdc.cab.inta-...LWR07556LL.FITS and http://sdc.cab.inta-...SWP08789LL.FITS from the IUE.

 

There's some stuff at Ondrejov, looks to a lower dispersion/resolution (I need to double check those two terms again), wavelength ranges as per the url "subfolder"

 

http://vos2.asu.cas....67/ui040066.vot

http://vos2.asu.cas....67/ui040067.vot

http://vos2.asu.cas....00/ui040069.vot

http://vos2.asu.cas....85/ui040071.vot

 

Just to prove there are circumstellar silicates there's ISO with the 10 micron bump

 

http://nida.esac.esa...obsno=574012070

 

http://cdsarc.u-stra...205736952561958 (no idea, 662 to 682 nm, Jena Observatory)

 

gaia dr3 LRS not worth the effort https://dc.zah.uni-h...992002051226752

 

And to finish off, you mentioned model spectra in one post, have you tried this?

 

http://pollux.graal.univ-montp2.fr/

 

I simply inputted the GAIA Teff of 4250 and log(g) -0.5 and zoomed in on Na I D and Halpha.

 

If you put in canonical M0 Iab details you should get a photospheric version of that???



#50 robin_astro

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Posted 19 December 2022 - 07:38 AM

 

It looks like spectra fits files are even more problematic than photometry and image ones in terms of what can be automatically used by applications.  There is a means in splat to choose what-centric, but I'm not clear if you did a heliocentric correction manually by assessing the MJD and working out the values yourself or whether the fits file had some info in there to enable you to do so, say your application simply using ra, dec and MJD to correct to heliocentric, which if I remember correctly are the three bits of data needed at base.

 

The ELODIE Archive fits header does indeed have the required information for our purposes here, using "reasonably standard" keywords.    For sub km/s accuracy though you would also need the observatory coordinates (Curiously not included in the header, though published elsewhere for OHP) as the "as measured" will actually be topocentric.

 

The BeSS  fits standard for spectra commonly used by amateurs has a flag to say if a heliocentric correction has been applied and a keyword for the value, though of course strictly we should be talking Barycentric here not Heliocentric as the planets impart a (very small) wobble to our Sun


Edited by robin_astro, 19 December 2022 - 07:44 AM.



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