Ada Ortiz-Carbonnell

	Ada Ortiz-Carbonnell

Ada Ortiz (ASP/HAO) has continued working on the topic of her PhD thesis, while also exploring other aspects of solar physics in collaboration with HAO staff.

While at HAO, she has showed that the intensity contrast of small photospheric magnetic elements was time independent during solar cycle 23. Since the nature of the observed contrast is directly related to the structure of the flux tubes making up these magnetic elements, this observed invariance with time supports the idea that the physical properties of the facular flux tubes do not vary with time, in particular with the solar cycle. This temporal invariability has often been assumed in the past-- there is no theoretical argument that implies that small magnetic features should have a different structure at solar minimum than at maximum -- but has never before been verified. This result was published in Ortiz et al., A&A, 452, 311, 2006.

She also expanded her research interests, and collaboration with Dr. Mark Rast has resulted in the study of the latitudinal variation of the photospheric intensity. In order to reproduce differential rotation profiles similar to those observed, solar differential rotation models must impose latitudinal variations of the entropy in the tachocline. This entropy variation is transported through the convection zone and translates into an expected temperature (or equivalently irradiance) difference of about 10 K between the equator and the poles (Rempel 2005, ApJ, 622, 1320). However, up to now photometers did not have enough photometric precision to detect such small intensity variations, and hence those variations had not been totally confirmed. The PSPT telescope (Precision Solar Photometric Telescope, Mauna Loa Solar Observatory, Hawaii ) has allowed us to accurately detect such latitudinal variations thanks to its 0.1% photometric precision per pixel, as well as observing an increase of the population of the smallest magnetic features towards the poles, likely due to their poleward accumulation produced by meridional circulation. This latitudinal variation of the photospheric intensity is entirely thermal and therefore not related to solar activity. The PSPT CaIIK images can be used as a proxy for the magnetic flux, as showed in Ortiz & Rast, MemSAIt, 76, 1018, 2005, and therefore we have used the best quality CaIIK images to mask out any activity found on the solar disk. This results are being the object of a publication to be submitted to ApJ (Rast & Ortiz, in preparation).

Also in collaboration with Dr. Rast she is working on the dependence of the facular and network contrast with other relevant parameters such as wavelength and spatial resolution, which will complement my previous work. The brightness signature of small magnetic features is a function of their heliocentric angle, size, averaged magnetic field, wavelength and spatial resolution.

Often contrast studies have analyzed the dependence of the contrast with position over the solar disk, and much less frequently with magnetic flux or wavelength; however the dependence with the resolution has been barely investigated although it plays an important role when comparing observations with MHD simulations (see Domingo et al., Adv Space Res., 35, 345, 2005). For this analysis we compare MDI full-disk and high-resolution images (2" & 0.625"/pixel respectively; wavelength: 676.8 nm) with PSPT measurements at three different wavelengths (1"/pixel; wavelengths: 393.5, 409.4 & 607.1 nm). This work is currently in progress and will be published in the following months (Ortiz & Rast, in preparation).

Funding Sources

This research is supported by the National Science Foundation.