The granulation noise appears to be correlated among the different wavelength ranges either in the visible or in the infrared regions. The prospects for planet detection and characterization with transiting methods are excellent with access to large amounts of data for stars. The granulation has to be considered as an intrinsic uncertainty as a result of stellar variability on the precise measurements of exoplanet transits of planets.
The full characterization of the granulation is essential for determining the degree of uncertainty on the planet parameters. In this context, the use of 3D RHD simulations is important to measure the convection-related fluctuations. This can be achieved by performing precise and continuous observations of stellar photometry and radial velocity, as we explained with RHD simulations, before, after, and during the transit periods.
A transit event occurs when the planet crosses the line of sight between the star and the observer, thus occulting part of the star. This creates a periodic dip in the brightness of the star. During the transit, the flux decrease is proportional to the squared ratio of planet and stellar radii. When the mass and radius of an exoplanet are known, its mean density can also be deduced and provide useful information for the physical formation processes.
Today and in the near future, the prospects for planet detection and characterization with the transiting methods are excellent with access to a large amount of data coming, for instance, from the NASA missions Kepler Borucki et al.
Space- and ground-based telescopes used for transit photometry require high photometric precision to provide accurate planetary radii, masses, and ages. Moreover, transit photometry also needs continuous time series data over an extended period of time. For all these reasons, it is necessary to go to space to monitor the target fields continuously with minimal interruptions.
However, with improved photometric precision, additional sources of noise that are due to the presence of stellar surface inhomogeneities such as granulation, will become relevant, and the overall photometric noise will be less and less dominated by pure photon shot noise.
In particular, granulation analysis of SOHO quiet-Sun data shows that the photometric variability ranges from 10 to 50 part-per-million ppm; Jenkins ; Frohlich et al. The granulation was observed for the first time on the Sun by Herschel , but Dawes coined the term granules. The granulation pattern is associated with heat transport by convection, on horizontal scales on the order of a thousand kilometers Nordlund et al.
The bright areas on the stellar surfaces, the granules, are the locations of upflowing hot plasma, while the dark intergranular lanes are the locations of downflowing cooler plasma. Stellar granulation manifests either on spatially resolved e. The best observational evidence comes from unresolved spectral lines because they combine important properties such as velocity amplitudes and velocity-intensity correlations, which produce line broadening.
This is interpreted as the Doppler shifts arising from the convective flows in the solar photosphere and solar oscillations Asplund et al. Similarly, correlations of velocity and temperature cause characteristic asymmetries of spectral lines as well as net blueshifts for main-sequence stellar types Dravins ; Gray The intensity ranges from [ 1.
The size ratio between the two images corresponds approximatively to the numerical box sizes. The purpose of this work is to study the impact of stellar granulation on the transit shape and retrieved planetary parameters e. We considered three prototypes of planets with different sizes and transit time lengths corresponding to a hot Jupiter, a hot Neptune, and a terrestrial planet. We used theoretical modeling of stellar atmospheres where the multidimensional radiative hydrodynamic equations are solved and convection emerges naturally.
These simulations take surface inhomogeneities i. They cover a substantial portion of the Hertzsprung-Russell diagram Magic et al. The intensity range is [ 0.
We generated 80 different synthetic solar-disk images to account for a granulation time-series of min We used the simulations Table 1 from the S tagger grid of realistic three-dimensional 3D radiative hydrodynamical RHD simulations of stellar convection for cool stars Magic et al. In a Cartesian box located around the optical surface i.
The simulation domains are chosen large enough to cover at least ten pressure scale heights vertically and to allow for about ten granules to develop at the surface; moreover, there are periodic boundary conditions horizontally and open boundaries vertically.
At the bottom of the simulation, the inflows have a constant entropy, and the whole bottom boundary is set to be a pressure node for p-mode oscillations. The simulations employ realistic input physics: the equation of state is an updated version of the one described by Mihalas et al.
They include continuous absorption opacities and scattering coefficients from Hayek et al. The abundances employed in the computation are the solar chemical composition by Asplund et al. Theses simulations have been used to compute synthetic images with the pure-LTE radiative transfer code O ptim 3D Chiavassa et al. The code takes into account the Doppler shifts that are due to convective motions. The radiative transfer equation is solved monochromatically using pre-tabulated extinction coefficients as a function of temperature, density, and wavelength.
O ptim 3D uses lookup tables with the same chemical compositions as the 3D RHD simulations as well as the same extensive atomic and molecular continuum and line opacity data as the latest generation of MARCS models Gustafsson et al.
The microturbulence is assumed to be zero i. The detailed methods used in the code are explained in Chiavassa et al. Table 2 Integrated wavelength bands computed.
We employed the tiling method explained in Chiavassa et al. These synthetic images have been used to map them onto spherical surfaces to account for distortions especially at high latitudes and longitudes by cropping the square-shaped intensity maps when defining the spherical tiles. Table 3 Prototypes of planets chosen to represent the planet transits. We generated 80 different synthetic stellar-disk images Fig.
This resulted in a simulated granulation time-series of min However, we assumed that this statistical representation is good enough to represent the changing granulation pattern during the planet transit.
The granulation pattern of the star may affect the photometric measurements during planet transit with two different types of noise: i the intrinsic timescale of the changes in granulation pattern e. These sources of noise act simultaneously during the planet transit, and we analyze them in the next sections. Note the use of the astronomical flux i.
Note also the logarithmic x - and y -axis scale. The green line is the temporal average profile. Central and bottom panels : enlargements for the Sun in the optical and infrared. The granulation pattern changes with time. Figure 4 displays the fluctuation of the intensity profiles for a particular cut in the synthetic disk images during a period corresponding to the transit duration of the prototype terrestrial planet 7 h, Table 3. In our approach, the solar disk intensity fluctuates during the transit by between [2.
Figure 5 top panel shows the number of photons is larger for the visible region with respect to the infrared, as can be expected by the behavior of the Planck function at these wavelengths. Moreover, the central and bottom panels show a clear dependence of the intensity with respect to wavelength ranges used. The noise is the fluctuation in the total number of detected photons, and it is for the granulation synthetic images and for the corresponding black body.
Figure 6 shows the ratio between the photon noise of the granulation images and the one from the black body. On the other hand, the K-dwarf granulation photon noise is systematically lower than the corresponding black body, even if it follows the same trends as the solar one. In the infrared, the situation is different: for both the Sun and the K dwarf, the photon noise is greater than the black-body noise for all wavelength ranges; moreover, K dwarf values are higher than the Sun owing to the lower effective temperature of the star and the consequent displacement of the radiation peak.
Granulation significantly affects the photon noise in various wavelength ranges compared to the black-body approximation, so that transit uncertainties based on the black-body approximation can overestimate or underestimate the uncertainties, depending on the wavelength range considered.
Furthermore, it is important to consider the change in the granulation pattern during the photometric measurements of transits like the one considered in this work, as developed in the next section. The wavelengths are taken from Table 2.
Chiavassa et al. Furthermore, they reported that the granulation causes intrinsic changes in the total solar irradiance over the same time interval as the Venus transit, arguing that the granulation is a source of an intrinsic noise that may affect precise measurements of exoplanet transits.
In short, observing granulation tissue in the bed of the wound means that the wound is progressing from the inflammatory phase of healing to the proliferative phase of healing. Several important cellular developments are occurring. Matrix metalloproteinases MMPs , which are so helpful in removing damaged tissue and bacteria from the inflammatory phase, have started to allow the formation of new blood vessels at the wound bed.
The number of MMPs is now starting to drop, which is a good thing because chronic MMPs can actually cause degradation of healthy proteins and growth factors and may delay healing. Cytokines, which are cells that are triggered by macrophages, are starting to increase in numbers and are telling the fibroblasts to get to work to start forming new tissue and blood vessels. You will also likely see a reduction in the four classic signs of inflammation: edema and erythema of the periwound, pain, and heat, which also indicate that the wound is progressing into the proliferative phase of healing.
Hypotrophic Granulation Tissue There are several variations of granulation tissue that you may encounter. You may find that the wound is filling in with new tissue; however, unlike the classic moist, beefy red tissue, it may appear smooth, pink, or even slightly pale. This is hypotrophic granulation tissue. I think of this as a wound that is desperately trying to heal, but something is standing in the way.
It indicates poor perfusion and often is caused by pressure, poor circulation, trauma, or infection. Make sure to offload any pressure, evaluate for potential trauma, and assess for and treat infection if present. This should help to alleviate hypotrophic granulation tissue and allow for healthier granulation tissue to develop.
Hypertrophic Granulation Tissue Another type of granulation tissue that you will likely observe is hypertrophic granulation tissue. I think of this as granulation tissue growth on overdrive. It will still have that classic moist, beefy red appearance, but it will be raised above the surface of the wound.
This will prevent the migration of epithelial cells across the center of the wound and will hinder healing. It is often a sign of excessive moisture or even infection, so make sure that you evaluate for this. After assessing for and treating these factors, some other interventions that you may consider are:. You may be wondering whether there are any interventions that you can implement to help encourage the formation of granulation tissue.
You can help encourage the proliferation of granulation tissue by:. With these factors in mind, once you do start to observe granulation tissue formation, it is important to ensure that the wound is protected.
This is a good time to start applying a collagen dressing or, for deeper wounds, negative pressure wound therapy. Try to space the dressings out as appropriate to every other day or even several times a week to provide a constant warm, moist environment for healing. With these tips in mind, the granulation tissue can continue to fill in the wound bed and allow the wound to contract and close in.
I hope that you, too, will celebrate a bit once you start to see the formation of granulation tissue because it is truly a beautiful thing. References 1. Physiology, Granulation Tissue. A high bioburden is postulated to alter the local environment of the wound, resulting in further lowering of the oxygen tension and accounting for the finding of increased neovascular formation around the foci of wound infection.
The hypergranulation tissue typically associated with high bioburden and infection is a brown-red color with a loose friable surface that bleeds easily. This may include wound dressings or treatments that typically impact an initial inflammatory response for healing and may result in increased exudate.
Proactively managing that temporary increase in exudate will aid in preventing hypergranulation tissue. Steroid impregnated tapes containing fludroxycortide may also be considered. As with other topical steroids, the therapeutic effect is primarily the result of its anti-inflammatory and antimitotic mode of action.
Occasionally, cautery with silver nitrate may be used to treat hypergranulation, but it is cautioned as it can be painful for the patient and caustic to healthy granulation tissue. The cauterization to the hypergranulated surface will necrose the superficial granulation tissue, which can then be wiped off. This technique should only be used if all else has been ineffective. Note that malignancy in a wound may be mistaken for hypergranulation.
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