1 and 2 Dimention Spectroscopy of G-band Bright Point

(paper 1) 2D-spectroscopic observations of G-band brigh

t structures in the solar photosphere– K. Langhans, W.Schmidt and A. Tritschler – AA 394, 1069, 2002

(paper 2) Diagnostic spectroscopy of G-band brightening

s in the photosphere of the sun– K. Langhans, W. Schmidt and T. Rimmele– AA 423, 1147, 2004

1. Introduction

1. Introduction

• G-band – 430nm– electronic transitions of the CH molecule

FeII (430.32nm) CH (430.34nm)

1. Introduction

• G-band bright points (GBP) – magnetic flux tube– Hot wall effect

• Radiative heating

• Photo-dissociation of the CH molecule by UV (?)

G-band White lightGBP

Hot wall

B

Optical surface

1. Introduction

• Bright Point Index (BPI)– Two type of G-band Bright Point

• An increased local continuum intensity small BPI

• Difference in CH and FeII line depression large BPI

I cont … continuum intensity at 430.33nm

I Fe lc … line core intensity of FeII (430.32nm)

I CH lc … line core intensity of CH (430.32nm)

brackets … spatial average over a reference region

G-band image

reference region

30 x 30 arcsec

line profile

dashed line … reference region

large BPI

small BPI

2. Observation

2. Observation (paper 1)

• German Vacuum Tower Telescope – in Observatorio del Teide, Tenerife

• Triple Etalon Solar Spectrometer (TESOS)– A single data set consists of 34 filtergrams– Wavelength step width : 1.62pm– Cadence : 17sec for the whole scan– FOV: 30 x 30 arcsec

• August 4, 2001 10:27UT• S8.3W3.3

2. Observation (paper 2)

• Richard B. Dunn Solar Telescope (DST) – in National Solar Observatory (NSO), SacPeak

• Horizontal Spectrograph (HSG) with AO– FOV: 40 x 10.5 arcsec

• October 6, 2001

• N20.2W12.3

3. Results (paper 1)

3. Results (paper 1)

(1) due to an increase of the local continuum intensity small BPI(2) due to a significant difference in CH and FeII line depression large BPI located in downflow region

(a) broadband at 431.1nm (b) narrowband continuum at 430.33nm

(c) velocity map (FeII)

3. Results (paper 1)

(d) CH-line core intensity (e) FeII-line core intensity (f) Bright Point Index

(1) due to an increase of the local continuum intensity small BPI(2) due to a significant difference in CH and FeII line depression large BPI located in downflow region

3. Results (paper 1)

only data with BPI > 0.2 Center-of-gravity plot for each BPI bin

The BPI is directory correlated with the downflow velocity

downflowupflow

3. Results (paper 1)

Change in line depression =G2 is related to large BPI value

Plot for C G-band >= 0.1

4. Results (paper 2)

Fig. 1. Broadband data.

G-band image (broadband 1 nm at 430.5 nm, slit jaw camera)

white light image (broadband 10 nm at 480 nm)

arcsec

slit

Fig. 2. Spectral data. Example for one scan. a) Continuum intensity at 430.41 nm, b)–e) Line core intensities of the analyzed absorption lines.

region around tracking point of AO

exposures of high quality used for analysis.

4. Resuts (paper 2)

Table 2. Averaged properties of bright points, based on the spectral data (Int.: interior; Surr.: surroundings; Ref.: reference).

(1) 46 bright points were identified in the 3 scans(2) Continuum contrast at 430.41nm of interior and surroundings are almost

equal line effect(3) Line depression CH

(1) Typical intergranular bright point(2) At the edge of a granule(3) At the edge of a pore

(1) (2) (3)

(1e)

(3f)

(2g) (3g)

(4) (5) (6)

(4) The largest(5) Unclear GBPs(6) Bright but not GBP

(6g)

(6h)

(4f)

(6f)

4. Resuts (paper 2)course of the BPI (solid curve) and the G-band intensity contrast (dashed curve)

velocity measurements (solid – CH, dashed – Fe I, dashed-dotted – Fe II)

(a) … typical GBP in downflow region(b)(c)(d) … upflow velocity at GBP

5. Discussion (paper 1 and 2)

granules

GBPs

Comparison of results for paper 1 and 2

granules

GBPs

Comparison of results for paper 1 and 2

granules

GBPs

down

up

Comparison of results for paper 1 and 2

5. Discussion

• Upflows in magnetic elements?– Previous results … down flow of magnetic elements

– Our results … Net downflows and upflows in individual bright points

• Convective collapse rebound and result in upward propagating shocks

• Flux tube with weak field strangths are unstable either a downflow or an upflow

Thank you

Fig. 7. Comparison of selected properties derived from synthetic spectra to observables. The bars indicate the range of values, observed for the bright point interior. Data points shifted to the left (thick symbols) refer to the CH line, data points shifted to the right (thin symbols) to Fe II and the centered symbols refer to Fe I.

Table 3. Top: continuum contrasts, Ccont, derived from synthetic spectra, with respect to the FAL C-model atmosphere. The listed values from observation refer to the average (maximum) over all observed bright point interiors with respect to the spectrum of the reference region. Bottom: filling factors derived from Eqs. (3) and (4).

Thank you again!

2. Observation (paper 2)

Table 1. Top: specification of the spectral data. Bottom: specification of the image data.Abbreviations: FF – Flat Field, SNR – Signal-to-Noise Ratio.

Fig. 4. Illustration of the velocity measurements. Vertical dashed lines indicate the borders of bright point interior and immediate surroundings, respectively. Top: BPI. Bottom left: intensity contrast, continuum intensity (solid), integrated G-band intensity (dashed). Bottom right: flow velocity.