These discrepancies are circumstantial evidence for the detection of spectral features attributable to a second photospheric component. LkCa 4 was observed for a total integration time of 90 s using an ABBA dither sequence along the slit to remove sky emission by differencing sequential exposures. <> As pointed out earlier, LkCa 4 has no detected companion from direct imaging, and its RV variations are consistent with starspot modulation, so any binary companion would have to have an exceptionally large luminosity (or mass) ratio, rendering it undetectable with our spectral inference methodology with the finite signal to noise available in the IGRINS data. A high fraction of the stellar surface may be covered in spots without inducing any photometric modulation, if the spots are located in circumpolar regions that always face towards our line-of-sight, in longitudinally symmetric bands, or in many isotropic small spots. We can now infer from our discussion so far the meaning of the Main Sequence in the HR diagram: The Main Sequence is the location in the HR diagram for stars in the first phase of their evolution, when they are fusing hydrogen in their cores. G. M. 2015, ApJ, 812, 128, Daemgen, S., Bonavita, M., Jayawardhana, R., Lafrenière, D., & L103, Preibisch, T. 2012, Research in Astronomy and Astrophysics, 12, 1, Pérez, F., & Granger, B. E. 2007, Computing in Science and Engineering, 9, 21, Rizzuto, A. C., Ireland, M. J., Dupuy, T. J., & Kraus, A. L. 2016, As expected, (2012). The synthetic models match the full spectrum reasonably well. Such estimates are limited by estimates of the radius since uncertainties in effective temperature and luminosity cause a wide range of radius estimates. 2014, AJ, 147, 82, Cottaar, M., Covey, K. R., Meyer, M. R., et al. (2014). Several orders in K−band were rejected due to poor spectral fits influenced by deep metal lines. Recent photometric monitoring of the Pleiades indicates that the anomalous colors scale with rotation rate, strengthing the case for magnetic-field induced starspots as the cause of the anomaly (Covey et al., 2016). This courseware module is part of Penn State's College of Earth and Mineral Sciences' OER Initiative. 3220, Downes, R. A., & Keyes, C. D. 1988, AJ, 96, 777, Edwards, S., Fischer, W., Hillenbrand, L., & Kwan, J. e-prints, arXiv:1609.04172, Grankin, K. N. 1998, Astronomy Letters, 24, 497, Grankin, K. N., Bouvier, J., Herbst, W., & Melnikov, S. Y. The two-temperature model assumed that the hot and cool components shared the same vsini and vz. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative For the median fill factor of 80%, the observed effective temperature would be 3180 K, with a range of 3070–3280 for 86% and 74% spot fill factors. (2014). 2005, ApJ, 635, 422, Cody, A. M., Stauffer, J., Baglin, A., et al. This drastic change in visible area of the hot spot (35% to 13%) is needed to explain the full ∼1 mag range in brightness, assuming no temperature change in either component. the Sun's coronal active regions. Transiting planets or eclipsing binaries passing in front of starspots (Desert et al., 2011) can break geometric degeneracies, providing estimates for the characteristic sizes and lifetimes of starspots or starspot groups, but the number of such transiting systems and demands of high photometric precision limit wider application. The stellar parameter ranges were logg∈[3.5,4.0] and [Fe/H]∈[−0.5,0.5]; the Phoenix model spectrum temperature range was Thot,Tcool∈[2700,4500]. Remarkably, the filling factor of cool photosphere exceeds 50%, with a best fit value of fcool=80±5%. Erroneous bulk opacities could be responsible for some of the scatter of fill factor distributions seen across different spectral orders, as in Figures 5 and 4. For the stars with the highest light curve amplitudes, this model shows that the spotted regions cover from 17 to 73% of the visible stellar hemisphere and that the mean temperature of the cool regions is 500−1400 K lower than the ambient photosphere. Astrophysical Observatory. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from Phoenix synthetic spectra to a high-resolution near-IR IGRINS spectrum. As the H-R diagram however shows that one is much more luminous than the other it must have a greater total power output therefore must have a much greater surface area - the more luminous star is bigger. (2008) photometry, following the color transformation prescribed by Landolt (1983) and applied by Grankin et al. (2006), where a K7 spectral type was adopted, and is higher than extinctions of AV=0.69 mag measured from optical photometry (Kenyon & Hartmann, 1995) and 0.35 mag measured by comparing optical spectra to young spectral templates (Herczeg & Hillenbrand, 2014). 377, Soderblom, D. R., Hillenbrand, L. A., Jeffries, R. D., Mamajek, E. E., The visible portion of the spectrum will be dominated by the warm patches. The V-band brightness reflects the instantaneous filling factor of the cool and hot components. (2016), the results shown here suggest that the contribution of starspots to pre-main sequence stellar evolution have been systematically underestimated. MG-S and GJH also thank Steve Saar, Lisa Prato, and Lynne Hillenbrand for valuable discussions about spots. Our results tentatively support the lower extinction obtained at optical wavelengths, although the template colors used to calculate extinction are uncertain and will need revision. Bouvier & Appenzeller, 1992; Bary & Petersen, 2014; Cottaar et al., 2014) and in comparisons of spectral types measurement based on TiO bands and those based on high-resolution blue spectra (see discussion in Herczeg & Hillenbrand, 2014). 1992, A&AS, 92, 481, Bouvier, J., Cabrit, S., Fernandez, M., Martin, E. L., & Matthews, In an HR diagram, spotted evolutionary model tracks at a given mass and age shift to higher luminosity and lower effective temperature. However, the near-IR spectrum is consistent with ∼ M2, when compared with main sequence dwarf stars (Vacca & Sandell, 2011). Journal, 122, 1954, O’Neal, D., Saar, S. H., & Neff, J. E. 1996, ApJ, 463, 766, Park, C., Jaffe, D. T., Yuk, I.-S., et al. Starspots are cooler than their surrounding photosphere and will, therefore, have a longer wavelength of peak emission. We should be able to detect an anticorrelation between the line center positions of spectral lines arising from the ambient photosphere and lines arising from cool starspots, since there is a zero-sum competition for solid-angle on the recessional and advancing stellar limbs. 2014), doi:10.5281/zenodo.12710, White, R. J., & Ghez, A. M. 2001, ApJ, 556, 265, Wilson, J. C., Henderson, C. P., Herter, T. L., et al.
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