Researcher: Alec Neal

Observations suggest that NSVS 2854398 is an eclipsing variable star of W Ursae Majoris type. This star is located at α=16:42:15.82 δ=+66:07:3.49 (J2000.0) and has the following alternate stellar designations: [GGM2006] 2854397, 2MASS J16421582+6607034, Gaia DR2 1636050933941404928. Star Field with stars used in ensemble differential photometry are shown in Figure 1.

Figure 1: Star field with ensemble stars used for differential photometry marked. The eclipsing variable star NSVS 2854398 is marked by the green target (T1). A rotationally variable star TYC 4196-1801-1 is marked green as T6.  All ensemble stars are marked by the red apertures and designated the labels C2-C5, C7-C20. If a V band magnitude is known, it is given with each comparison. Field scale is given on the left side and top of the image. Image is a representative image taken with the BSUO 20-inch telescope. Further details for each comparison star are given below in Table 1. Further details regarding the telescope and detector used can be found on our BSU Observatory page.
Identifier Position (J2000.0) Magnitudes
(1) (2) (3) (4) (5) (6) (7)
ID Catalog α δ B V Rc
C2 TYC 4196-1648-1 16:42:34.909 +66:13:21.47 12.57 ± 0.29 11.13 ± 0.09 —
C3 TYC 4196-1395-1 16:41:58.612 +66:16:36.65 12.82 ± 0.27 12.10 ± 0.19 —
C4 TYC 4196-2203-1 16:42:51.723 +66:17:41.27 12.28 ± 0.18 11.59 ± 0.12 —
C5 TYC 4196-2335-1 16:43:58.961 +66:12:06.91 12.88 ± 0.27 12.47 ± 0.23 —
†T6 TYC 4196-1801-1 16:42:12.935 +65 53 01.75 †11.80 ± 0.11 †11.02 ± 0.11 —
C7 TYC 4196-1720-1 16:42:27.438 +65:54:44.19 11.89 ± 0.11 11.30 ± 0.09 —
C8 TYC 4196-1870-1 16:44:19.934 +65:52:47.83 12.72 ± 0.28 11.69 ± 0.15 —
C9 TYC 4196-1583-1 16:44:33.859 +65:57:47.87 12.38 ± 0.24 11.00 ± 0.07 —
C10 TYC 4196-1815-1 16:40:20.259 +65:52:39.60 12.85 ± 0.30 11.65 ± 0.14 —
C11 TYC 4196-1572-1 16:41:08.223 +66:02:21.52 13.36 ± 0.45 11.32 ± 0.11 —
C12 — 16:40:47.546 +66:01:04.71 — — —
C13 — 16:41:14.170 +66:05:07.34 — — —
C14 — 16:42:11.662 +66:04:42.72 — — —
C15 — 16:41:53.855 +66:06:39.00 — — —
C16 — 16:42:04.976 +66:06:00.30 — — —
C17 — 16:41:23.105 +66:09:53.79 — — —
C18 — 16:42:21.474 +66:09:19.16 — — —
C19 — 16:42:43.291 +66:06:59.24 — — —
C20 — 16:43:35.854 +66:04:39.64 — — —

Table 1: List of comparison stars used in differential ensemble photometry analysis. First column gives the comparison designation. Columns (2) & (3) give the Right Ascension (α) and Declination (δ) of the comparison in J2000.0. Columns (3)-(6) report measured Johnson B (B), Johnson V (V) and Cousins R (Rc) band magnitudes. Magnitudes are used to calibrate the magnitudes of the target star. Calibrated magnitudes are used to determine magnitudes in the Johnson-Cousins system.
†Rotationally variable star. Given magnitudes were not used in the photometry.

We have observed this star with the Ball State University Observatory (BSUO) 20-inch (0.6-m) telescope in the B, V, and Rc bandpasses. All stellar photometry is performed by the AstroImageJ (AIJ) software package. All photometry is performed with similar ensemble stars. If a calibrated magnitude for a comparison star is known, then it is used by AIJ to calibrate the magnitude for the target star. Folded light curves are shown for B, V, and Rc in Figure 2.

Figure 2: Folded color light curve for NSVS 3792718. All photometry is differential ensemble photometry performed by the AstroImageJ (AIJ) software package. Top panel shows folded V-band curve. Bottom panel shows folded (B-V) color curve. All magnitudes are calibrated by the known magnitudes of the ensemble stars. Error bars are not shown for clarity.

By analyzing the B-V at quadrature (Φ = ± 0.25) and accounting for interstellar reddening (Av=0.181), the color index of the system was determined to be (B-V)0 = 1.068 ± 0.098, corresponding to a primary star surface temperature of 4716 ± 165 K, and a spectral type of about K4 V. This temperature was calculated using the polynomial coefficients given in Flower 1996.

Best fitting Wilson-Devinney (WD) Models
All modeling is performed using the PHysics Of Eclipsing BinariEs (PHOEBE) (v0.31a) software package.  PHOEBE is a graphical user interface (gui) to the WD code that is used to model binary stars. Figure 4 shows the best fit WD model without spots. Figure 5 shows a model fit with a single spot.
Figure 4: Best-fit WD model fit with no spots (red solid curve) to the folded light curve for differential Johnson B (left panel), V (center/middle panel), and Cousins R (right panel) band magnitudes.  In each panel the top panel shows the folded light curve for B, V, or R bands, and the bottom panel shows the deviation of the observed values from the best-fit WD model.Figure 5: Best-fit WD model fit with a single spot (red solid curve) to the folded light curve for differential Johnson B (left panel), V (center/middle panel), and Cousins R (right panel) band magnitudes.  In each panel the top panel shows the folded light curve for B, V, or R bands, and the bottom panel shows the deviation of the observed values from the best-fit WD model. The location (coordinates) of the spot is specified in Table 3.

Best-fit Model Parameters
Below is Table 3, which lists parameters and their values derived in the analysis of this system via the methods discussed above. Note that the ns subscript represents values/errors without spots (“no spots”), and the subscript s denotes values/errors with spots. See the table caption for more details and/or clarification.

Parameter Symbol [unit] Valuens Errorns Values Errors
(1) (2) (3) (4) (5) (6)
Period P [days] 0.290428 0.003007 0.290428 0.003007
Epoch T0 [HJD] 2458308.729867 0.0001683 2458308.729867 0.0001683
Inclination i [°] 85.30 3.33 86.32 3.33
Surface Temp. Teff,1 [K] 4716 190 4716 190
Teff,2 [K] 4406 190 4415 190
Surface Potential Ω1,2 [-] 5.75 0.04 5.78 0.04
Mass Ratio q [-] 2.39 0.03 2.43 0.03
Distance d [pc] 184 28 184 28
Spot Colatitude Φ2 [°] 90
Spot Longitude λ2 [°] 27
Spot Radius ρ2 [°] 6
Temp. Factor τ2 [-] 1.24
Stellar Mass‡ M1 [M☉] 0.749 0.053 0.749 0.053
M2 [M☉] 1.792 0.129 1.82 0.131
Stellar Radius‡ R1 [R☉] 0.79 0.79
R2 [R☉] 1.17 1.18
Semi-major Axis‡ a [R☉] 2.52 0.062 2.53 0.063

Table 3: System parameters of NSVS 2854398.  Column (1) gives the name of the parameter, (2) gives the parameter symbol and [unit], (3) and (4) give the parameter value and error, respectively, without spots (ns), while (5) and (6) give the parameter value and error with spots (s). Any blanks in the table denote data which is, as of the most recent entry, unknown and/or unavailable.
‡These values were calculated using the the equations in Harmanec (1988). These equations assume our star(s) are main sequence, which is suspect. We only include the values as crude estimates, as spectral and radial velocity data will be required to obtain more certain values.

Phase Animation

Figure 6: Phase animation of NSVS 2854398, playing at 20 frames per second (approx. ×5000 speed). Individual frames were gathered from the model created in the PHOEBE program, and were compiled into an animation using the website ezgif.com.

Presentations
Poster presentations and talks given by Alexander J. Neal (Alec Neal) at national, regional and local conferences for NSVS 2854398 are given below.

  1. NSVS 2854398 and Recent Developments, Physics & Astronomy colloquium. November 21, 2019.
  2. NSVS 2854398, a Short-period W UMa with Total Eclipses, American Astronomical Society, 236th Annual Meeting. June 1, 2020.

Contact Information
All members of the Variable Star Research group are enthusiastic researchers with a passion for the work performed by the group. We are always happy to discuss any research projects and are always looking for like-minded and enthusiastic collaborators. For more information regarding any of the aforementioned research activities or the research activities of the Variable Star Research Group, please do not hesitate to contact Robert Berrington.