NSV 19335 (a.k.a. GSC 3834:180)
This web page is devoted to a description of observations and (amateur) modeling of the above red dwarf. It exhibits chaotic variability and many flares. Sometimes it varies sinusoidally with a period of 0.7262 day, and at other times it varies chaotically (with a hint of the same periodicity).  Last Updated 2013.08.06.
Internal link to most recent light curves  (Return to 19335 Observing Project web page)
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). Here are some APASS magnitudes: B=14.252, V=12.564, g'=13.402, r'=11.936, i'=10.634. 2MASS mags: J=8.588, H=7.993, K=7.757. The star's SED (at bottom of this page) can be fit with Teff = 3100 K (i.e., M4). NSV 19335 is not in the Hipparcos catalog, so we don't know it's distance (& therefore can't determine from its brightness if it's on the main sequence).

The PAWM2 project consists of advanced amateurs searching for WD variability that could be explained by an exoplanet reflecting WD starlight. NSV 19335 was noticed to be variable because it was located near a targeted WD. Nine advanced amateur observers have contributed over 200 hours of observations of this star in an attempt to understand its variability. Characterizing the star's variability has been a frustrating experience because sometimes it is sinusoidal and at other times it is chaotic, as the following two phase-folded plots show:


Figure 1. Phase-folded LCs for data when the star varies sinusoidally (left panel) and when it varies differently (right panel).

The 9-member observing team endeavored to characterize the pattern of when it was sinusoidal from the other times by conducting intense observations during 2013 May 12 to 24 (see: http://brucegary.net/pawm2/19335/19335.html). We investigated the possibility that when it wasn't sinusoidal with the 0.7262-day period it was varying with a different period, but this search was unsuccessful. There is a hint that during the non-sinusoidal times there was some residual variability with the same 0.7262-day periodicity; at those times it simply wasn't sinusoidal. Due to the star's active flaring it was necessary to identify flare data and not use it in the search for non-flaring variability patterns. Two modes were identified: SINE (sinusoidal) and MESA (non-sinusoidal). Here's a record of which mode the star was in versus observing date:


Figure 2. Mode versus observing date.

There is hint of regularity for switching between SINE mode and MESA mode. Below is a phase-fold plot of the same data using a switching period of 11.3 days (and phase reference of Apr 11):


Figure 3. Phase-folded mode status, suggesting that mode switchings occur at an interval of ~ 11 days.

What physical model could cause this behavior? Consider a debris cloud that scatters with minimal absorption (e.g., ice crystals). The cloud is in an orbit with a period of 11.3 days. The cloud extends along the orbit in an arc less than ~ 180 degrees long. When the cloud is not in our line-of-sight to the star the mode is SINE. When the cloud intersects the line-of-sight it scatters but does not obscure (because the particles don't absorb). The scattering occurs along the entire length of the cloud so the brightness level is essentially unaffected by the starspot's lower surface brightness. This means that during MESA mode the average brightness is the same as the average brightness of SINE mode. Even during SINE mode the debris cloud is contributing to the system's total flux, but it is not modulating the 17.4-hour rotational variation produced by the starspot.

We were hampered in our attempt to obtain overlapping LC data from 2 or more observers by the fact that we began the observing project late in the star's observing season. A tentative plan was made to resume observations in 2014, prior to the observing season mid-point date (March 24). With each observer capable of producing long LCs it should be possible to improve on the characterization of brightness variability as well as achieving multiple observer overlap to confirm variability type.

In spite of the physical model described above, we feel discouraged about the prospects for understanding this star before the next observing season (2014 February) when we have to decide if there is merit in continuing to observe NSV 19335. We therefore seek advice from a professional astronomer having experience with irregular variables on the matter.

Anyone reading this should now go to another web page: http://brucegary.net/pawm2/19335/19335.html, where you should navigate down to the section "Summary of Light Curve Results." That's where we present a more detailed description of our futile attempts to understand this irregular variable. 









Arminski's 5-Year Observations of NSV 19335

Here
is a 5.0-year light curve based on a 189-image set (of EG UMa, including 162 with NSV 19335), and recently re-processed by observer AAM using a consistent set of reference stars.


Figure 2. A recent re-processing by Arminski of 162 images with NSV 19335 present, showing a brightness variation range of ~0.2 magnitudes (with a V-band filter). [Note that this is a phase plot, with a 5-year period; thus, each data point is present twice.]

2013 Observations of Variability

GBL observed NSV 19335 on 9 dates in April, 2013. Five of these were with a Cb-band filter (clear with blue-blocking). Starting Apr 28 AAM began long observing sessions using an Rc filter.
Observers AAM and GBL are coordinating observations with a Rc filter and same 3 reference stars (using APASS Rc mag's) in order to produce a better-coverage stability plot and phase-fold light curve. GBL Rc observations began May 1. Empirical magnitude offsets have been determined for placing data with the various filters on a internally-consistent magnitude scale (set for Rc-band). Here's a LC for the Cb- and Rc-band data.

  
Figure 3a. Variability using a Cb- and Rc-band filters, with flares removed.


Figure 3b. Variability using a Cb- and Rc-band filters, showing agreement between observers during a smooth rise and fall (x = 29) and a large and abrupt rise and fall (x=32).

Here's an attempt at phase folding in search of a repeating pattern:


Figure 4.
Phase-folded light curve for Rc-band and Cb-band magnitudes. Keep in mind that flares will produce occasional bright outliers, and even though an attempt was made to delete the obvious flare activity data there may be a residual of high data points in this plot. It is inescapable that if this is the principal component of variation there are other components that may in fact be non-periodic. Hence, this may in fact be an irregular variable. The period of 0.784 days (18.87 hours) could be associated with the star's rotation.

The phase-fold sinusoidal fit to the lower envelope, with departures in the direction of greater brightness suggests that there are at least two components accounting for variability: 1) a rotational component with P = 0.7864 days (18.87-hours) and 2) another longer period component of activity. To investigate this second component of activity the "residuals" off the 0.7864-day sinusoidal fit are plotted versus date and are then phase folded, as shown in the next two figures.

 
Figure 5. Rc-band magnitudes using same reference stars and two observers (AAM & GBL). An empirical adjustment of 0.74 mag to AAM data has been applied (which could be due to the fact that none of the GBL and AAM data have been "CCD transformation" corrected).  


Figure 6. Phase-folded light curve for Rc-band & Cb-band "residuals" off of the sinusoidal fit to the lower envelope (Fig. 3). The extra activity appears to have a repeating interval of 1.634 days. 

More observations are needed before accepting that the "residual" activity has a 1.634-day repeating pattern. If it is confirmed then we might consider that NSV 19335 is a M-dwarf/M-dwarf double star, in which at least one component has a strong magnetic field and somewhat erratic activity.  Or maybe NSV 19335 is a binary consisting of a M-dwarf and a very cool white dwarf that is interacting with the M-dwarf.


Present Light Curve Observations
   (Return to 19335 Observing Project web page)






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(Mag's not adjusted by 0.074 mag)


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The following LCs were obtained with a Cb filter (clear with blue-blocking).



   oot   No flares.


   oot   Big flare.


Another flare.


No flares.


The noisy section in the middle is probably due to saturation fro too long exposures.

I count 5 flares are present during these 43.4 observing hours. The four g' and i' observing sessions (not shown, 34.8 hours) had 4 flares. The flare rate is therefore 9.0 3.0 per 78.2 hours, or 2.8 0.9 flares per 24 hours od observation.

Spectral Energy Distribution



Figure 7. 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 WD component.

Proposed New NSV 19335 Observing Project

http://brucegary.net/pawm2/19335/19335.html

References

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



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WebMaster:
B. Gary.  This site opened:  2013.04.22.  Last Update:  2013.05.25 UT