On the intensity contrast of solar photospheric faculae  and network elements

Ortiz, A.; Solanki, S. K.; Domingo, V.; Fligge, M.

doi:10.1051/0004-6361:20020500

Cited by 104 publications

(199 citation statements)

References 47 publications

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“…The main observational evidence is as follows. First, faculae are known to be more abundant near the poles (Erofeev 1980;Unruh et al 1999;Ortiz et al 2002), however they are also present in active regions (Ortiz et al 2002). The study of radio limb brightening as a function of position angle has shown that the emission is stronger at the polar region and also at the equatorial limb (Fig.…”

Section: Discussionmentioning

confidence: 98%

“…Faculae are mainly observed within active regions and near the poles. Several authors have reported a significant increase in the number of faculae toward the poles (Ortiz et al 2002;Erofeev 2001), and the intensity contrast of faculae has been shown to increase near the poles (Wang & Zirin 1987;Lawrence 1988;Unruh et al 1999 and references therein). Several authors have reported the existence of regions of enhanced temperatures at radio wavelengths in the polar zones of the Sun (Kundu & McCullogh 1972;Efanov et al 1980;Riehokainen et al 1998Riehokainen et al , 2001Shibasaki 1998;Nindos et al 1999;Gelfreikh et al 2002).…”

Section: Introductionmentioning

confidence: 99%

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Temporal and angular variation of the solar limb brightening at 17 GHz

Selhorst

Silva

Costa

et al. 2003

A&A

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Abstract. In order to better understand the atmosphere structure of the Sun, we have analyzed over 3000 daily maps of the Sun taken at 17 GHz from the Nobeyama Radioheliograph (NoRH) from 1992 through 2001, focusing on the excess brightness temperature observed near the limb. The purpose of this work is to characterize the limb brightness in two ways: (i) study the temporal variation of the intensity and radial width of polar brightening; and (ii) measure the brightness distribution along the limb as a function of position angle and compare it with data at other wavelengths throughout the solar cycle. The mean intensity of the polar regions were found to be approximately 13% and 14% above quiet Sun levels at the North and South poles, respectively. Moreover, the polar brightenings are strongly anti-correlated with solar activity (as measured by sunspot number). The radial width of the excess brightness is slightly over 1 arcmin for both polar regions. Only a small variation with the solar cycle was observed during the decline of last maximum, that is, the Southern polar brightening was found to be both wider and brighter than the Northern one for the 23rd cycle. As for the angular variation of the limb brightening, for a month during a period of minimum activity, it reaches 25% above quiet Sun levels at the poles, ∼15% near the equator, and 10% at intermediate regions. Hα images also show brightening enhancements at the polar regions for the same period. We also found a strong anti-correlation between the radio polar brightenings and the coronal holes seen in soft X-ray images from 1992 to 2001. There seems to be a strong association of the radio limb brightening at 17 GHz with faculae. The implications of these correlations are discussed.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Temporal and angular variation of the solar limb brightening at 17 GHz

Selhorst

Silva

Costa

et al. 2003

A&A

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“…It is therefore difficult to directly use the published contrasts found in the literature (for example Frazier 1971;Lawrence 1988;Ermolli et al 2007), because they are very sensitive to the way plages are defined. The large dispersion between individual plages, as well as the differences between plages and network structures (Foukal et al 1991;Worden et al 1998;Ortiz et al 2002Ortiz et al , 2006) also adds to the uncertainty of these measurements. To realize a consistent simulation, we computed the photometric contribution of each kind of structure (spots, plages, network) and compared it with the observed total solar irradiance (hereafter TSI).…”

Section: Spot and Plage Observed Contrastsmentioning

confidence: 99%

Using the Sun to estimate Earth-like planets detection capabilities

Meunier¹,

Desort²,

Lagrange³

2010

A&A

270

394

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Aims. Stellar activity produced by spots and plages affects the radial velocity (RV) signatures. Because even low activity stars would produce such a signal, it is crucial to determine how it influences our ability to detect small planetary signals such as those produced by Earth-mass planets in the habitable zone (HZ). In a recent paper, we investigated the impact of sunlike spots. We aim here to investigate the additional impact of plages. Methods. We used the spot and plage properties over a solar cycle to derive the RV that would be observed if the Sun was seen edgeon. The RV signal comes from the photometric contribution of spots and plages and from the attenuation of the convective blueshift in plages. We analyzed the properties of the RV signal at different activity levels and compared it with commonly used activity indicators such as photometry and the Ca index. We also compared it with the signal that would be produced by an Earth-mass planet in the HZ. Results. We find that the photometric contributions of spots and plages to the RV signal partially balance each other out, so that the residual signal is comparable to the spot signal. However, the plage contribution due to the convective blueshift attenuation dominates the total signal, with an amplitude over the solar cycle of about 8-10 m/s. Short-term variations are also significantly greater than the spot and plage photometric contribution. This contribution is very strongly correlated with the Ca index on the long term, which may be a way to distinguish between stellar activity and a planet. Conclusions. Providing a very good temporal sampling and signal-to-noise ratio, the photometric contribution of plages and spots should not prevent detection of Earth-mass planets in the HZ. However, the convection contribution makes such a direct detection impossible, unless its effect can be corrected for by methods that still need to be found. We show that it is possible to identify the convection contribution if the sensitivity is good enough, for example, by using activity indicators.

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“…We attempt to correct this bias using a median-filter derived from 100 sunspot-free dates in 2008 and 2009. A similar approach was considered for older magnetograms in Ortiz et al (2002). As can be seen in the resulting filter shown in Fig.…”

Section: Modeling Irradiancementioning

confidence: 99%

Solar irradiance variability: a six-year comparison between SORCE observations and the SATIRE model

Ball

Unruh

Krivova

et al. 2011

A&A

108

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Aims. We investigate how well modeled solar irradiances agree with measurements from the SORCE satellite, both for total solar irradiance and broken down into spectral regions on timescales of several years. Methods. We use the SATIRE model and compare modeled total solar irradiance (TSI) with TSI measurements over the period 25 . We discuss the overall change in flux and the rotational and long-term trends during this period of decline from moderate activity to the recent solar minimum in ∼10 nm bands and for three spectral regions of significant interest: the UV integrated over 200−300 nm, the visible over 400−691 nm and the IR between 972−1630 nm. Results. The model captures 97% of the observed TSI variation. This is on the order at which TSI detectors agree with each other during the period considered. In the spectral comparison, rotational variability is well reproduced, especially between 400 and 1200 nm. The magnitude of change in the long-term trends is many times larger in SIM at almost all wavelengths while trends in SIM oppose SATIRE in the visible between 500 and 700 nm and again between 1000 and 1200 nm. We discuss the remaining issues with both SIM data and the identified limits of the model, particularly with the way facular contributions are dealt with, the limit of flux identification in MDI magnetograms during solar minimum and the model atmospheres in the IR employed by SATIRE. However, it is unlikely that improvements in these areas will significantly enhance the agreement in the long-term trends. This disagreement implies that some mechanism other than surface magnetism is causing SSI variations, in particular between 2004 and 2006, if the SIM data are correct. Since SATIRE was able to reproduce UV irradiance between 1991 and 2002 from UARS, either the solar mechanism for SSI variation fundamentally changed around the peak of cycle 23, or there is an inconsistency between UARS and SORCE UV measurements. We favour the second explanation.

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On the intensity contrast of solar photospheric faculae and network elements

Cited by 104 publications

References 47 publications

Temporal and angular variation of the solar limb brightening at 17 GHz

Temporal and angular variation of the solar limb brightening at 17 GHz

Using the Sun to estimate Earth-like planets detection capabilities

Solar irradiance variability: a six-year comparison between SORCE observations and the SATIRE model

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