AKARI observations of ice absorption bands towards edge-on young stellar objects
AKARI observations of ice absorption bands towards edge-on young stellar objects
复制标题
AKARI 对边缘年轻恒星物体冰吸收带的观测
DOI：
10.1051/0004-6361/201015999
复制
发表时间：
2012
影响因子：
6.5
通讯作者：
Y
中科院分区：
文献类型：
--
作者：
Aikawa;Y
低质量年轻恒星（YSO）的星周盘和包层含有大量的冰。目的为了研究低质量年轻恒星周围星周冰的组成和演化，我们观测了8颗0-II类年轻恒星的近红外吸收带，并对它们的冰吸收带进行了分析，发现它们的冰吸收带的大小与太阳系中的彗星相似，但它们的冰吸收带的大小与太阳系中的彗星相似。其中7个与边缘盘有关。方法我们使用AKARI上的红外照相机（IRC）的棱镜模式进行了无狭缝光谱观测，这使我们能够获得从2.5μm到5μm的完整近红外光谱，包括CO2带和H2O带的蓝翼，这是从地面无法获得的。我们开发了程序来仔细处理星云状目标的光谱。用多项式基线拟合光谱以得到吸收光谱。分子吸收带，然后拟合与冰吸收带的实验室数据库，考虑到仪器的线轮廓和光谱分辨率的棱镜dispersion element.ResultsTowards的0-I类源（L1527，IRC-L1041-2，和IRAS 04302），H2O，CO2，CO，和XCN的吸收带被清楚地检测到。CO2冰和CO冰相对于H2O冰的柱密度比分别为21−28%和13− 46%。如果XCN是OCN−，它的柱密度相对于H2O冰高达2 - 6%。在0-I类源和HV Tau附近探测到4.1μm的HDO冰特征。未检测到3.5μm附近的CH伸缩模式特征，提供了相对于H2O的26%（L1527）和42%（IRAS 04302）的CH 3OH丰度上限。我们尝试性地探测到OCS冰对IRC-L1041-2的吸收。对于0-I类源，检测到的特征应该主要来自冷包层，而CO气体和OCN−可能来自靠近原恒星的区域，那里有温暖的温度和紫外线辐射。我们检测到H2O冰带朝向ASR 41和2 MASSJ 1628137-243139，这是边缘上的II类磁盘。我们还检测到HV Tau、HK Tau和UY Aur方向的H2O冰和CO2冰，并初步检测到HK Tau和UY Aur方向的CO气体特征。
ContextCircumstellar disks and envelopes of low-mass young stellar objects (YSOs) contain significant amounts of ice. Such icy material will evolve to become volatile components of planetary systems, such as comets in our solar system.AimsTo investigate the composition and evolution of circumstellar ice around low-mass young stellar objects (YSOs), we observed ice absorption bands in the near infrared (NIR) towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks.MethodsWe performed slit-less spectroscopic observations using the grism mode of the InfraRed Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5μm to 5μm, including the CO2band and the blue wing of the H2O band, which are inaccessible from the ground. We developed procedures to carefully process the spectra of targets with nebulosity. The spectra were fitted with polynomial baselines to derive the absorption spectra. The molecular absorption bands were then fitted with the laboratory database of ice absorption bands, considering the instrumental line profile and the spectral resolution of the grism dispersion element.ResultsTowards the class 0-I sources (L1527, IRC-L1041-2, and IRAS 04302), absorption bands of H2O, CO2, CO, and XCN are clearly detected. Column density ratios of CO2ice and CO ice relative to H2O ice are 21−28% and 13−46%, respectively. If XCN is OCN−, its column density is as high as 2−6% relative to H2O ice. The HDO ice feature at 4.1μm is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5μm provide upper limits to the CH3OH abundance of 26% (L1527) and 42% (IRAS 04302) relative to H2O. We tentatively detect OCS ice absorption towards IRC-L1041-2. Towards class 0-I sources, the detected features should mostly originate in the cold envelope, while CO gas and OCN−could originate in the region close to the protostar, where there are warm temperatures and UV radiation. We detect H2O ice band towards ASR41 and 2MASSJ 1628137-243139, which are edge-on class II disks. We also detect H2O ice and CO2ice towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features towards HK Tau and UY Aur.