Researcher: Alexander Thomas

Observations suggest that NSVS 2827877 is an eclipsing variable star of W Ursae Majoris type. This star is located at α=16:27:44.2 δ=+56:45:59.2 and has the following alternate stellar designations: TYC 3881-579-1, NSVS 2827877, [GGM2006] 2827876, GSC 03881-00579, 1RXS J162743.9+564557, 2MASS J16274415+5645592, [DCO2008] T-Dra0-00959, Gaia DR1 1431129007637668096 and, Gaia DR2 1431129011933593088. Star field with the target star and comparison stars used in ensemble differential photometry are shown in Figure 1.
NSVS 2827877 Star FieldFigure 1: Star field with ensemble stars used for differential photometry marked. The variable star NSVS 2827877 is marked by the green target (T1). All ensemble stars are marked by the red apertures and designated the labels C2-C6. If a B band magnitude is known, it is given with each comparison. Field scale is given on the left side 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.
(J2000.0) Magnitudes
Comparison Catalog α δ B V Rc
C2 TYC 3881-886-1 16:27:31.00 +56:44:03.62 12.86 ± 0.24 12.18 ± 0.17 —
C3 TYC 3881-623-1 16:26:02.22 +56:40:25.37 11.41 ± 0.07 10.82 ± 0.06 —
C4 — 16:28:25.274 +56:48:37.81 — — —
C5 — 16:27:09.496 +56:53:01.79 — — —
C6 — 16:26:33.645 +56:58:20.93 — — —

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.
We have observed this star with the Ball State University Observatory (BSUO) 20-inch (0.5m) 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 for Johnson V and (B-V) color are shown in Figure 2.
Color Light CurveFigure 2: Folded color light curve for NSVS 2827877. 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.

Observed Minus Calculated (O-C) Time of Minimum Analysis
Times of minimum light were determined for the nights observed, and are given in the following table along with Observed minus calculated (O-C) times of minimum. All reported errors are 1σ error bars.

[HJD] [days]
Time of Minimum Error Eclipse (O-C) Error
2458246.77938 ±0.00023 primary 0.0 ±0.00023
2458262.75043 ±0.00068 secondary -0.001164 ±0.000718
2458623.73827 ±0.00033 secondary -0.002296 ±0.000402
2458274.77216 ±0.00033 primary 0.000240 ±0.000402

Table 2: Heliocentric Julian dates [HJD] for times of minimum (first column) are reported along with 1σ errors bars (second column). All times of minimum light are first determined for each filter (B, V, and Rc) light curve, and are determined by the method described by Kwee & van Woorden (1976). Similar times of minimum for differing filter light curves are averaged together and reported in column Times of Minimum. Eclipses are designated by primary for the primary eclipse and secondary for the secondary eclipse in the Eclipse column (third/middle column). Values of (O-C) (fourth column) are given in units of days along with 1σ errors (fifth column).
An observed minus calculated (O-C) time of minimum light analysis was performed and is shown in Figure 3. The analysis was performed using the reported times of minimum light given in table 2. The O-C values are determined by the following linear ephemeris and are given in the above table.

Tmin [HJD] = 2458246.77938 + 0.3293240 · E (1)
±0.00023 ±0.000633

Figure 3: Observed time of minimum minus calculated time of minimum (O-C) plot with best-fit linear linear line (solid line) versus epoch number (E). Error bars are 1σ error bars assuming the period of the system is known with out errors. All O-C values are given in units of days and are determined by the linear ephemeris given in equation (1). Best-fit linear line is determined by an unweighted linear least squares analysis. Slope of best-fit line represents a negligible correction to the ephemeris given in equation (1).

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 with two star spots included. Figure 5 shows a graphical representation of the stellar surface.

Figure 4: Best-fit WD model fit with spots (red solid curve) to the folded light curve for differential B (left panel), V (center panel), and Rc (right panel) band magnitudes.

Figure 5: Stellar models showing best-fit stellar models for the light curves shown in Figure 3. Orbital phases (Φ) are given in each panel and are Φ = 0 (upper-left panel), Φ = 0.25 (upper-right panel, quadrature), Φ = 0.5 (lower-left panel), and Φ = 0.75 (lower-right panel, quadrature). The final model includes two stellar spots (shown) with one spot on each stellar component and are apparent at orbital phases Φ = 0.5 and Φ = 0.75.

 

Final System 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 with no spots, and the subscript s denotes values/errors with spots. See the table caption for more details and/or clarification.

(1) (2) (3) (4) (5) (6)
Parameter Symbol [unit] Valuens Errorns Values Errors
Period P [days] 0.329324 0.000633 “ “
Epoch T0 [HJD] 2458246.77938 0.00023 “ “
Inclination i [deg]
Surface Temp. Teff,1 [K] 5599 231
Teff,2 [K]
Stellar Mass‡ M1 [M☉] 1.04 0.075
M2 [M☉]
Stellar Radius‡ R1 [R☉] 1.12
R2 [R☉]
Semi-major Axis‡ a [R☉]

Table 3: System parameters of NSVS 2827877. 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). Some values are independent of spots, so the second instance is marked with a quotation mark (“). 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.

Presentations
Poster presentations and talks given at national, regional and local conferences for NSVS 2827877 are given below.

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.