NSV 19335 Observing Project
Bruce L. Gary, Hereford Arizona Observatory
This web page describes a project of coordinated observations of an M dwarf star that has puzzling variations in multi-band observations. Observations by a team of European and American amateurs is underway. Observing dates and filter use is being coordinated in a way that will address the reality of departures from a single sinusoidal variation. It is anticipated that observations will be confined to 2013 May and June.  
Time of Update: Thursday, May 25, 20 UT                                                                                Links:  Light Curves   Satellite IR images: Europe  USA 
Current Status: Observing is "ON HOLD" until the complicated variability can be understood better. We may resume next April, when obs'g sessions will be longer. 
Previous Night:

List of dates when useable observations were obtained.

 Session #1
 		Session #2
 		Session #3
 		Session #4
 		Session #5
 		Session #5.5
 Session #6
 		Session #7
 		Session #8
 		Session #9

Sunday
 May 12/13
 		Monday
 May 13/14
 		Wednesday
 May 15/16 		Thursday
May 16/17
 		Saturday
May 18/19
Sunday
May 19/20
 Monday
May 20/21
 		Wednesday
May 22/23
 		Friday
May 24
Ogmen

cloudy cloudy Rc, 18.0-22.2 on 18th
Rc, 20.0-22.0


Arminski
 		rain
 rain
 V, 21.5-26.3, 15th
 cloudy OVC
 V, 21.8-25.3



Zambelli
 cloudy cloudy cloudy cloudy OVC
vacation


Salas
 		V, 21.9-27.5, 12th
 V, 20.2-25.0
 cloudy cloudy raining
OCV


Gregorio
 		down for repair
 down for repair V, 2.9-9.9, 16th
 cloudy BKN, not obs'g
BKN
 Rc, obs'g

Gary
 		V, 02.8-11.5, 13th
 V, 02.8-9.8, 14th
 V, 2.8-9.9, 16th
 V, 2.8-10.0, 17th
 Rc, 4.2-11.2 on19th
r', 03.0-11.3
 r', 3.3-10.2


Wiggins
 		cloudy
 cloudy
 cloudy cloudy cloudy
Rc, 4.3-10.1
Rc, 4.5-10.1
Foote J
 		on travel
 on travel cloudy cloudy cloudy
on travel


Foote C
 		on travel
 on travel cloudy cloudy cloudy
on travel


Key: CLR = clear, SCT = scattered clouds, BKN = broken clouds, OCV = overcast; f = "forecast", c = "currently". Entries consist of: "filter assignment/sky condition" before observing session starts; "filter used/length" after session completed.  If anyone needs to e-mail me with assurance of immediate reply (e.g., filter question), use this address: brucegary9@gmail.com                       
East Longitude (Lat)
 Observer Name (Code)
 Location
 Telescope & Filters E-mail
+033.725 (+35.258)
 Yenal Ogmen (OYE)
 North Cyprus
 14": B, V, Rc,Ic
 green.island.observatory at live.com
 more info
+014.550 (+53.4??)
 Andrzej Arminski (AAM)
 Szczecin, Poland
 08": V, Rc
 aa at aarminski.com.pl
 more info
+010.008 (+44.104)
 Roberto Zambelli (ZRO)
 Sarzana, Italy
 16": V, LRGB
 robertozambelli .rz at libero.it
 more info
-000.936 (+41.629)
 Javier Salas (SJ2)
 Saragossa, Spain
 14": B, V, R, I, Cb
 jsalas at orange.es
 more info
-008.817 (+38.733)
 Joao Gregorio (GJL)
 Atalaia, Portugal
 12": V,Rc,Ic,L,Cb
 crisostomo.gregorio at oninet.pt
 more info
-110.238 (+31.452)
 Bruce Gary (GBL)
 Hereford, Arizona; USA
 11": B, V, Rc, Ic, Cb, g', r', i', z'
 brucegary9 at gmail.com
 more info
-112.296 (+40.641)
 Patrick Wiggins (WPK)
 Stansbury Park, Utah; USA
 14": B, V, R, I, C (Schuler)
 paw at wirelessbeehive.com
 more info
-112.435 (+37.029)
 Jerry Foote (JFEA)
 Kanab, Utah; USA
 24": B, V, Rc, Ic, C
 jfoote at kanab.net
 more info
-112.436 (+37.028) Cindy Foote (FCN)
 Kanab, Utah; USA
 16": V, V, Rc, Ic, C
 cfoote at kanab.net
 more info


Figure 1. Location of stars suitable for reference based on a combination of their redness and brightness. Use any subset of these (and no other stars).
FOV = 18.6 x 12.4 'arc; north up, east left. [Notice new star numbering!]
Ref#
 B
 V
 Rc
 Ic
 g'
 r'
 i'
 z'
 B-V










1
 13.033
 11.554
 10.385
 10.775
 12.291
 11.084
 10.634
 10.385
 1.479
2
 14.487
 13.571
 13.065
 12.650
 14.004
 13.303
 13.098
 13.027
 0.916
3
 16.156
 14.816
 13.987
 13.414
 15.523
 14.298
 13.935
 13.787
 1.340
4
 12.593
 11.546
 11.007
 10.528
 12.043
 11.257
 10.988
 10.850
 1.047
5
 15.865
 14.716
 14.027
 13.480
 15.320
 14.309
 13.972
 13.829
 1.149
6
 14.452
 13.460
 12.939
 12.501
 13.927
 13.183
 12.955
 12.868
 0.992
7
 11.876
 10.884
 10.373
 9.891
 11.344
 10.615
 10.343
 10.192
 0.992
8
 16.662
 15.337
 14.490
 13.877
 16.029
 14.802
 14.399
 14.226
 1.325
9
 12.869
 11.912
 11.421
 10.929
 12.361
 11.659
 11.377
 11.227
 0.957
10
 13.178
 12.410
 12.012
 11.643
 12.745
 12.225
 12.066
 12.008
 0.768
11
 12.355 11.607 11.232 10.864 11.956
 11.444
 11.286
 11.220
 0.748
The above magnitudes are to be used for establishing NSV 19335's magnitude (note correction to Ref#11, 2013.05.14).

Data submission text files can be comma delimited, tab delimited or fixed format space delimited. There should be at least two columns: JD (245????.???? format) and target magnitude ( ??.???? format). Use a header based approximately on the following:

StartDate   : 2013.05.12
Object      : NSV 19335
Observer    : Gary, Bruce (GBL)
E-mail      : 123-at-brucegary.net
Location    : Arizona
Latitude    : +31.452
ELongitude  : -110.237
Aperture    : 14-inch
Filter      : V
Exposure    : 40 sec
Comment     : 10 ref stars, 10 used for calibration
Comment     : Col 1 = JD (exposure midpoint)
Comment     : Col 2 = target magnitude
Comment     : Col 3 = RMS
Comment     : col 4 = airmass
Comment     : 99.9999 values are rejected outliers

Columns 3 and 4 are optional.

Some web sites for satellite cloud cover images: 
    Europe:  http://www.sat24.com/en/?animation=true&ir=True 
    Spain/Portugal: http://sat24.com/en/sp?ir=true
    Europe Rain Forecast:  http://www.sat24.com/foreloop.aspx?type=1
    USA IR: http://www.wunderground.com/US/Region/US/2xIRSatellite.html
    USA IR: http://www.wunderground.com/US/Region/US/2xVisSatellite.html
    USA IR: http://www.wunderground.com/cgi-bin/satblast/satBlast?lat=31.280794&lon=-110.431282&width=640&height=480&zoom=6&SatType=VIS&Map.x=360&Map.y=111
    Gobal Cloud Loop:  http://www.sat24.com/world.aspx

Summary of Light Curve Results


Figure 2. V-mag versus date (days past May 12.0). Flares deleted. The two departures from a purely sinusoidal variation are indicated by thick dashed grey traces. They might be due to cancellation of variations by members of a binary pair that rotate with slightly different periods. The sinusoidal component of variation would then be due to the addition of variations from the two dwarfs that reinforce each other (as illustrated by Fig. 4). This very unusual variation pattern is exactly what we're trying to confirm.


Figure 3. This phase-fold illustrates the problem we're trying to understand. Not all data obey a simple sinusoidal variation. The interval identified in the previous figure as non-sinusoidal is displayed using small cross symbols.


Figure 4. Example of a multi-day light curve for a binary model in which both have spots but rotate with different periods. It illustrates that for a few days one periodicity exists, followed by a short interval of no periodicity, followed by another interval with the first periodicity shifted by 1/2 phase. Such a star system would be classified as an "irregular variable."

Before we began to use V-band as a group, Andrezej and I observed with Rc filters. Rc-band counterparts to Fig's 2 and 3 are shown below.


Figure 5. Rc-mag versus date (starting with data from May 1).


Figure 6. This Rc-band phase-fold light curve exhibits a lot of too-bright data, presumably due to transient activity possibly related to flaring. The interval identified in the previous figure as non-sinusoidal is displayed using small cross symbols.


Figure 7. Dates with Sine Mode data only. RC mag's were adjusted using equation: mag = 12.587 + (Rc-mag - 12.587) * 1.41.

But there's another mode which I'll call "MesaMode." Consider superimposing the MesaMode data on the previous plot, shown below.


Figure 7. The black symbols are from Mesa Mode dates.


Figure 8. This type of graph can be used to look for a pattern for the "mode changes" ("sine" to "mesa") and also the association of flares with mode. So far we can say that flares occur during both modes, but are more common during the Mesa Mode dates. Also, modes last a few days.

Star Spot Model

The fact that the Rc-band amplitude had to be multiplied by 1.41 to achieve a match with V-band measurements is consistent with the variation being produced by a star spot. In fact, this ratio can be used to derive the temperature of the star spot interior compared with the exterior. The average surface temperature is 3060 K, as determined from the SED. For a spot temperature of 2448 K the V-band flux decreases to 12.1% of its surroundings while the Rc-band flux is reduced to 16.8% of the surroundings. In other words, the effect of such a star spot on flux as it rotates into view will be 16.8/12.0 = 1.41 times greater at V-band than Rc-band. Let's adopt this dT = -612 K temperature difference for the derivation of spot size.

Consider a star spot with dT = -612 K and solid angle of 1% of the star's solid angle. The flux ratio for the presence of the star spot being near star center compared with the star spot not be present would be (0.99 + 0.01 * 0.121), or  0.99121. In other words, "minimum flux" / "maximum flux" = 0.99121, which corresponds to a change of 9.59 mmag. For NSV 19335 the change from maximum to minimum flux is twice the semi-amplitude, or 160 mmag. The solid angle of the spot must therefore be 16.7 times larger than 1%, which is 16.7 %. If the spot is near the apparent star center then this corresponds to a spot radius of 9.6 degrees.


________________________________________________________________________________________________________________________________________________________

Background

NSV 19335 is located 8.0 'arc north of WD1213+528 (EG UMa), at 12:15:39.5 +52:39:09. It was discovered to be variable by Shugarov (1984), who noted in a report on nearby Case 1 (aka, EG UMa) that "It is worth noting that the star No. 4 on our chart [referring to NSV 19335] is possibly a slow variable with an amplitude not exceeding 1 m." As far as I have been able to determine this is the only publication relating to NSV 19335. The AAVSO database has 152 observations of NSV 19335 by Andrzej Arminski (AAM, of Poland). These V-band observations exhibit a 0.2-mag range of values. AAVSO's VSX catalog lists this objects variability type as "LB" (Slow irregular variables of late spectral types (K, M, C, S); as a rule, they are giants (CO Cyg). This type is also ascribed, in the GCVS, to slow red irregular variables in the case of unknown spectral types and luminosities. ).

NSV 19335 has a proper motion of 103.5 "arc/year (moving east). APASS magnitudes (B=14.252, V=12.564, g'=13.402, r'=11.936, i'=10.634) and 2MASS mags (J=8.588, H=7.993, K=7.757) yield a spectral energy distribution (SED) of a M dwarf with Teff = 3135 K. The B-V = 1.688 places this star in the top 1.5% of reddest stars. NSV 19335 is not in the Hipparcos catalog, so we don't know it's distance (& therefore can't determine its absolute magnitude, and therefore can't determine if it's on the main sequence).

Recent Observations of Variability

Observer AAM (Andrzej Arminski, Poland) has observed NSV 19335 at V-band for ~ 5 years, and his are the only data in the AAVSO archive. AAM recently conducted observations with a Rc-band filter. Here's his phase-folded light curve for these data, with a period solution that seems solid.

  
Figure B1. Phase-folded variability of Rc-band observations by AAM, showing a period solution of 0.732 day (17.57 hours).

Observer GBL (Bruce Gary, Arizona) observed NSV 19335 with a Cb filter (clear with blue blocking) on 5 dates in April. These observations exhibit variability that cannot be explained using the same ephemeris that accounts for the AAM Rc data.


Figure B2. GBL observations with a Cb-band filter, in April, showing no correlation with the phase-fold sinusoid solution for the AAM Rc-band data (gray trace).

Finally, GBL observed with a Rc-band filter in May and found some agreement with AAM's Rc-band data.


Figure B3. GBL's Rc-band observations, phase-fold sinusoid solution for the AAM Rc-band ephemeris (gray trace).

In the above figure the large difference in average magnitude may be explained by our not correcting for "CCD transformation equations." In other words, the AAM and GBL "telescope system passbands" when using a Rc-band filter may differ enough that the very red star (in relation to the same reference stars) are really being measured at different effective wavelengths, causing the very red target star to appear to have different Rc-band magnitudes. The same argument can be used to account for the slight difference in amplitude of variation between AAM and GBL. The brightness difference of GBL data at phase 0.1 (~ 30 mmag) is statistically significant, suggesting real changes versus observing date, but atmospheric extinction differences between the two observing dates may account for this as an "apparent" difference (i.e., not real).

NSV 19335 is often very active as a flare star, as the following light curve shows.

 
Figure B4. Three or four flares occur during this 6.6-hour observing session with a Cb-band filter.

Flares are always greater at shorter wavelengths, so at B-band the above major flare must have been dramatic. Flare activity implies a strong magnetic field, and magnetic fields are also associated with star spots. Star spots produce variations that are greater at shorter wavelengths, which is especially apparent for red stars. Such spots might account for the the difference in variation amplitude with wavelength (seen above), assuming spots produce the variation so far observed.  
 
Spectral Energy Distribution

Here's a SED for NSV 19335, based on APASS and 2MASS magnitudes.
Figure B5. Spectral Energy Distribution (SED), using a M-dwarf SED function (Barnard's Star), fitted to measured magnitudes (APASS and 2MASS).

 This SED has no evidence of the presence of a hot WD component, nor is there evidence for an accretion disk or a cooler star (e.g., brown dwarf), but we need photometry data at longer wavelengths than K-band to be sure that it has neither.   Using this SED's solution for Teff = 3100 K, and assuming main sequence status, we can estimate that Mstar = 0.2 × Msun, and Rstar = 0.26 × Rsun.

It looks like photon flux (proportional to Lamda × Flux_lambda) varies strongly within most filter passbands. The next several graphs show the SED with linear scales for the purpose of illustrating this.


Figure B6a. Same SED plotted with linear/linear scales.


Figure B6b. Same SED showing wavelength range for typical CCD filter bands.


Figure B6c. Same SED showing filter response function (referenced to outside atmosphere) for typical BVRcIc filter bandpasses, CCD QE, telescope transmissions and atmospheric extinction.

Notice in the above graph how much photon flux changes within some of these bands.  Ic has an extreme range of photon flux from the turn-on wavelength of 0.7 micron to 1.05 micron.  V has the least amount of change across it.


Figure B6d. Same SED showing filter response function (referenced to outside atmosphere) for SDSS g'r'i'z'Cb filter bandpasses (Astrodon filters), CCD QE, telescope transmissions and atmospheric extinction. 

This graph (above) illustrates one of the virtues of the SDSS filter set: each band has abrupt wavelength turn-ons, and all but z' have abrupt turn-offs. This means that the range of photon fluxes for a star like NSV 19335 is approximately the same across the bandpass. For example, consider the ratio of photon flux at the longest wavelength to shortest. For Ic (cf. Fig. 6c) this ratio is 3.3, whereas for i' it is 2.6. For the Rc-band filter this ratio is 6.0, whereas for r'-band it is 2.5. Therefore, the SDSS filters should have smaller systematics related to SED shape than the Johnson-Cousins BVRcIc filters. Also, the SDSS filters provide a "cleaner" distinction between the information produced by one band versus another compared with use of the BVRcIc bands.

Proposed Observing Plan

The proposed observing plan is based on answering several questions that are raised by the current set of puzzling data.

1) In order to remove doubt that any one observations is flawed, and can't be used for assessing variability, we should have at least two observers observing at the same time with the same filter. European observers are best at producing quality light curves, so I propose recruiting the most advanced European astronomy observers, with demonstrated exoplanet transit LC experience, and assigning them the this task. I propose initially tasking European observers to coordinate observations with Rc filter, and using the same 3 reference stars that AAM and I have identified for use. After each observer establishes agreement with a consensus, this task will be considered complete.

2) We want to determine an ephemeris with the best credibility possible, at one wavelength (at first). This means we should have overlapping LCs from observers at a range of longitudes (and same filter). The best filter for this may be Ic-band (or z'-band), which should have a smaller slope of brightness versus wavelength than any of the shorter wavelength bands. Referring to the above SED, J-band would be ideal for this purpose, but no amateurs that I know about have such a CCD/filter system. Depending on filter availability of the recruited observers, we will probably settle on using Rc-band. Longitudes from Poland to Utah and Arizona should be sufficient for this task.

3) Does NSV 19335 exhibit variations at short wavelengths, such as B-band, that are uncorrelated with variations at long wavelengths, such as Ic- or z'-band? I have a z'-band filter and can work with an observer in the USA who can observe simultaneously with a B-band filter.

NSV 19335 has an "observing season" centered on March 24, so we won't be able to obtain useful observations after about mid-June.

Observing Procedure and Data Reporting

Observers will process their image sets with an agreed upon list of reference stars (any subset of the 10 shown below). A light curve will be constructed, as well as a text file with the data (JD & mag), and both will be sent to me (GBL, Bruce Gary) using e-mail (either attached, or embedded).

I'll use the txt-file to construct phase-folded LCs of everyone's data. I'll also maintain a light curve archive web page. The beginning section of this web page can serve to show who observed when, etc (as in previous observing campaigns).

Any publication that results from this project will include all observers as co-authors, ranked by my measure of how much observing was contributed.

Finder Chart and Reference Stars


Figure B7. Star field centered on NSV 19335, FOV = 18.6 x 12.4 'arc; north up, east left.  

Ref#
 B
 V
 Rc
 Ic
 g'
 r'
 i'
 z'
 B-V










1
 13.033
 11.554
 10.385
 10.775
 12.291
 11.084
 10.634
 10.385
 1.479
2
 14.487
 13.571
 13.065
 12.650
 14.004
 13.303
 13.098
 13.027
 0.916
3
 16.156
 14.816
 13.987
 13.414
 15.523
 14.298
 13.935
 13.787
 1.340
4
 12.593
 11.546
 11.007
 10.528
 12.043
 11.257
 10.988
 10.850
 1.047
5
 15.865
 14.716
 14.027
 13.480
 15.320
 14.309
 13.972
 13.829
 1.149
6
 14.452
 13.460
 12.939
 12.501
 13.927
 13.183
 12.955
 12.868
 0.992
7
 11.876
 10.884
 10.373
 9.891
 11.344
 10.615
 10.343
 10.192
 0.992
8
 16.662
 15.337
 14.490
 13.877
 16.029
 14.802
 14.399
 14.226
 1.325
9
 12.869
 11.912
 11.421
 10.929
 12.361
 11.659
 11.377
 11.227
 0.957
10
 13.178
 12.410
 12.012
 11.643
 12.745
 12.225
 12.066
 12.008
 0.768
11
 13.837 13.230 11.232 10.864 13.537
 12.982
 12.009
 11.220
 0.607
Table 1. These magnitudes are to be used for establishing NSV 19335's magnitude.


Figure B8. Magnitude/B-V color diagram, showing that 10 stars have a combination of redness and brightness that render them suitable reference stars for NSV 19335.

The 10 stars with a best combination of redness and brightness are identified in the finder map (Fig. 6) and their magnitudes are given in the table (above).

Observers
East Longitude (Lat)
 Observer Name (Code)
 Location
 Telescope & FiltersData sub E-mail
+033.725 (+35.258) Yenal Ogmen (OYE)
 North Cyprus 14": B, V, Rc,Ic green.island.observatory at live.com more info
+014.550 (+53.4??)
 Andrzej Arminski (AAM)
 Szczecin, Poland
 08": V, Rc
 aa at aarminski.com.pl
 more info
+010.008 (+44.104)
 Roberto Zambelli (ZRO)
 Sarzana, Italy
 16": V, LRGB
 robertozambelli .rz at libero.it
 more info
-000.936 (+41.629)
 Javier Salas (SJ2)
 Saragossa, Spain
 14": B, V, R, I, Cb
 jsalas at orange.es
 more info
-008.817 (+38.733)
 Joao Gregorio (GJL)
 Atalaia, Portugal
 12": V,Rc,Ic,L,Cb
 crisostomo.gregorio at oninet.pt
 more info
-110.238 (+31.452)
 Bruce Gary (GBL)
 Hereford, Arizona; USA
 14": B, V, Rc, Ic, Cb, g', r', i', z'
 19335 at brucegary.net
 more info
-112.296 (+40.641)
 Patrick Wiggins (WPK)
 Stansbury Park, Utah; USA
 14": B, V, R, I, C (Schuler)
 paw at wirelessbeehive.com
 more info
-112.435 (+37.029)
 Jerry Foote (JFEA)
 Kanab, Utah; USA
 24": B, V, Rc, Ic, C
 jfoote at kanab.net
 more info
-112.436 (+37.028) Cindy Foote (FCN)
 Kanab, Utah; USA
 16": V, V, Rc, Ic, C
 cfoote at kanab.net
 more info
Table 2. Observer information.





References

Shugarov, S. Yu., 1984, IBVS N2612.


Return to NSV19335 web page with more NSV 19335 info (lots of LCs)
Go to PAWM2 web page

WebMaster: B. Gary.  This site opened:  2013.05.08.  Last Update:  2013.05.25 UT