凌星類熱木行星大氣的地面觀測研究

陳果

(中國科學(xué)院紫金山天文臺(tái) 南京 210008)

博士學(xué)位論文摘要選登

凌星類熱木行星大氣的地面觀測研究

陳果?

(中國科學(xué)院紫金山天文臺(tái) 南京 210008)

太陽系外凌星類行星是目前進(jìn)行系外行星大氣研究的最佳目標(biāo)之一.在特殊的軌道構(gòu)型條件下才可以進(jìn)行凌星主食和次食的觀測,它們分別對應(yīng)于行星位于宿主恒星正前方和背后兩種情況.相應(yīng)的觀測可以產(chǎn)生大氣透射譜和熱發(fā)射譜,在大氣組成和溫度結(jié)構(gòu)的觀測研究中扮演著重要的角色.基于這兩種譜線性質(zhì),本文使用馬普2.2 m望遠(yuǎn)鏡的GROND(Gamma-Ray Burst Op tical and Near-infrared Detector)設(shè)備對3顆熱木星的次食進(jìn)行了測光觀測，又使用帕洛瑪5.1 m海爾望遠(yuǎn)鏡的DBSP(Double Spectrograph)、TSpec(Trip le Spectrograph)和COSM IC(Carnegie Observatories Spectroscopic M u ltislit and Im aging Cam era)設(shè)備對另兩顆熱木星的主食進(jìn)行了光譜觀測,以求搜尋到任何可能的來自行星大氣的信號(hào)、并用于了解擁有不同物理性質(zhì)的熱木星的大氣多樣性.

本文第3章至第5章分別對WASP-5 b、WASP-46 b和WASP-43 b的次食的測光觀測進(jìn)行了詳細(xì)說明.3顆熱木星的次食均在K波段被顯著探測到，同時(shí)在J和H波段還存在一些可能性較高的非顯著探測或者3σ上限.這些近紅外次食測量所反映的是來自行星晝半球大氣的熱發(fā)射,由于相應(yīng)波段的不透明度較低,所探測的大氣層也相應(yīng)較深.這是首次對WASP-5 b和WASP-46 b進(jìn)行近紅外熱發(fā)射探測,我們利用GROND測得的數(shù)據(jù)顯示W(wǎng)ASP-5 b的較深層大氣呈大致等溫的狀態(tài),溫度約為2700 K.當(dāng)與斯皮策空間望遠(yuǎn)鏡獲取的中紅外數(shù)據(jù)結(jié)合在一起分析時(shí),我們發(fā)現(xiàn)在數(shù)據(jù)可探測壓強(qiáng)范圍內(nèi)不存在逆溫現(xiàn)象.斯皮策數(shù)據(jù)反映的是較高層大氣,對應(yīng)的溫度約為1900 K.在大氣模型分析中,氧豐大氣與觀測數(shù)據(jù)并不相符,而碳豐模型雖能很好地進(jìn)行數(shù)據(jù)擬合,卻不能保證能量平衡.WASP-46 b的觀測顯示其晝半球大氣很可能也處于等溫狀態(tài),溫度大約在2386 K,雖高于全局熱再分布的平衡溫度,但在誤差范圍內(nèi)仍與局部最高平衡溫度相符.我們在K波段測得的WASP-43 b的熱發(fā)射信號(hào)確認(rèn)了此前其他研究組在2.09μm窄帶和KS波段獲得的測量結(jié)果.觀測表明,這3顆熱木星在晝夜半球間的熱再分布效率都非常低.我們還分析了WASP-46 b和WASP-43 b在光學(xué)波段的次食測量結(jié)果,如果這些信號(hào)并非來自系統(tǒng)效應(yīng),那么很可能意味著高層大氣中存在反射云層.此外,借助于GROND多波段同步觀測能力,我們還測得了一條WASP-43 b晝夜交界時(shí)大氣寬帶透射譜.但限于寬帶的光譜分辨率和測量精度,目前還難以獲得大氣組成的有效信息,這顯示了相應(yīng)研究工作使用光譜觀測的必要性.

在第6章和第7章中,我們分別總結(jié)了針對HAT-P-1 b和HAT-P-32 b的主食進(jìn)行的光譜觀測.恒星星光因穿透行星晝夜交界處的高層大氣而攜帶了相應(yīng)的化學(xué)組成信息.我們通過分析HAT-P-1 b的透射譜,發(fā)現(xiàn)了鉀共振雙線的存在,這是首次在1顆系外行星的光譜中分辨出鉀雙線特征.所測得的鉀雙線只存在窄線心輪廓,缺乏理論中預(yù)期的壓力致寬線翼,暗示可能存在云霾.我們的光學(xué)透射譜覆蓋了310–520 nm和610–1000 nm,對其的分析顯示:HAT-P-1 b高層大氣中不存在TiO和VO,也不存在純?nèi)瘥惿⑸湓砌?結(jié)合哈勃望遠(yuǎn)鏡W FC3設(shè)備在1.1–1.7μm獲取的透射譜,我們可以排除其大氣中存在光學(xué)厚云的可能性.現(xiàn)有的數(shù)據(jù)表明其高層大氣很可能由近太陽豐度組成,并含有Na、K、H2O和CH4等成分.在針對HAT-P-32 b的觀測中,我們測得的光學(xué)透射譜在一定程度上呈現(xiàn)了TiO/VO的吸收特征,但多云大氣的情況并不能被排除.

Transiting exop lanets are currently am ong them ost favorable targets for atm ospheric studies of exop lanets.Such special orbital geom etry enables transits and secondary eclipses to be observable,which refer to the events when p lanetsmove in front of or behind host stars.Corresponding observations would result in transm ission spectroscopy or em ission spectroscopy,which are extrem ely powerful in the investigation of atm ospheric com positions and tem perature structures.Based on these two techniques,this thesispresentsphotometric observations on the secondary eclipses of three hot Jupiters using GROND(Gamma-Ray Burst Opticaland Near-infrared Detector)mounted on the MPG 2.2m telescope,and spectroscopic observations on the transits of another two hot Jupiters using DBSP(Double Spectrograph),TSpec(Triple Spectrograph),and COSM IC(Carnegie Observatories Spectroscopic Multislit and Imaging Camera)mounted on the Palomar 5.1 Hale telescope.The primary goal is to search for any detectable signals of atm ospheric origin,and to study potential atmospheric diversity among hot Jupitersw ith various physical properties.

The photometric observations on the secondary eclipses of WASP-5 b,WASP-46 b, and WASP-43 b are detailed in Chapter 3,4,and 5,respectively.The dips of secondary eclipse have been significantly detected for all three hot Jupiters in the K band,along w ith some possible detection or 3σupper lim it in the J or H band.These near-infrared eclipse detection measures the thermal em ission from the deep dayside atmosphere.It is the first time to detect any therm al em ission in the near infrared for WASP-5 b and WASP-46 b.Our GROND measurements indicate a roughly isothermal temperature profile of around 2700 K in the deep layers of WASP-5 b’s dayside atmosphere.Together w ith Spitzer observations,which probe higher layers w ith a tem perature of around 1900 K,a tem perature inversion is ruled out in the probed pressure range.W hile an oxygen-richm odel is unable to explain all the data,a carbon-rich model provides a reasonable fit but violates the energy balance.The GROND em ission measurements of WASP-46 b also suggest an isothermal tem perature profile for its dayside atm osphere.Our K-band measurement for WASP-43 b confirm s previous detections obtained in the 2.09μm narrow band and KSband.A ll three hot Jupiters seem to have very poor day to nightside heat redistribution. Furtherm ore,we present the analysis of optical eclipse measurements for WASP-46 b and WASP-43 b,which are either false positivesor indication of reflective cloudsat high altitude. Additionally,thanks to the simultaneous multi-band observing capability of GROND,a broad-band transm ission spectrum is derived for WASP-43 b.Lim ited by current spectral resolution and precision,the atm ospheric com positions can not be distinguished,indicating the necessity of the spectroscopic observations.

In Chapter 6 and 7,the spectroscopic observations on the transits of HAT-P-1 b and HAT-P-32 b are summarized,respectively.Stellar light that has been transm itted through

planetary term inator atmosphere carries information of atmospheric com positions.We report the first detection of the K resonance doublet absorption in HAT-P-1 b.This is the first time to resolve the K doublets in any p lanet.The K absorption profile consists of only narrow coreswhile lacks pressure-broadened w ings,indicating clouds or hazes.Our optical transm ission spectrum,covering the wavelength ranges of 310–520 nm and 610–1000 nm, rules out the presence of TiO and VO and the p resence of pure Rayleigh-scattering hazes. Together w ith the 1.1–1.7μm transm ission spectrum derived by HST/W FC3,we also rule out the possibility of optically thick clouds.The current combined dataset iswellexp lained by a nearly solar-abundance atm osphere of Na,K,H2O,and CH4.For HAT-P-32 b,the measured optical transm ission spectrum shows signatures of TiO/VO absorption to some degree,but a cloudy atmosphere is not comp letely ruled out.

G round-based Observational Characterization of Transiting Hot-Jup iter A tm osphere

CHEN Guo

(Pu rp le M oun tain O bserva to ry,Chinese A cadem y o f Sciences,Nan jing 210008)

10.15940/j.cnki.0001-5245.2016.05.011

?2014-07-06獲得博士學(xué)位,導(dǎo)師:紫金山天文臺(tái)王紅池研究員;guochen@pm o.ac.cn