[PCG22-P08] Band 3 continuum and CO molecular line observations towards HD 142527 with ALMA
Keywords:protoplanetary disk, HD 142527, radio observation, continuum emission, molecular line emission, ALMA
We present the observational results of dust continuum, 13C16O J = 1 − 0, and 12C16O J = 1 − 0 emissions from the disk surrounding a Herbig Fe star, HD 142527, taken in Band 3 (∼ 100 GHz) with ALMA in its Cycle 2. This study is the first to show the spatially and spectrally resolved J = 1 − 0 rotational emissions of the CO molecules. The synthesized beams of the observations are approximately 50 mas, and the spectral resolutions for the CO molecular observations are 0.04 km s−1.
The dust disk is observed to be divided into two parts, an inner disk and an outer disk, by a dust-depleted region. While the former is not resolved by the beam, the outer disk is detected out to a radius of 2 arcsec from the central star, and depending on the position angle its inner radius ranges from 0.5 arcsec to 1 arcsec. HD 142527 is known for its crescent-like outer disk in the millimeter and longer wavelengths, and our observation reveal the same non-axisymmetric features, where the disk northern region is brighter than the southern region. The peak intensity of the outer disk, as a function of position angle P.A. and radius r, shows a maximum of 11.5 mJy beam−1 at P.A. = 10°, r = 1.1 arcsec, and a minimum of 0.2 mJy beam−1 at P.A. = 237°, r = 1.3 arcsec; the contrast in intensity is thus about 60 between the two direction. The gas spatial distribution traced by 13C16O J = 1 − 0 line emission resembles that of the J = 3 − 2 of the same molecule; its integrated intensity is more axisymmetric and does not differ by more than a factor of two in the azimuthal direction.In addition, 13C16O is most probably optically thick as its brightness temperature is as high as 40 K even at 1 arcsec from the star. On the other hand, the distribution of the 12C18O J = 1 − 0 integrated intensity, unlike its J = 3 − 2 counterpart which shows an axisymmetric distribution around the central star, departs substantially from the azimuthal symmetry; its emission concentrates in the northern part of the disk that is about 25 K in brightness temperature, with almost no appreciable detection above a signal-to-noise ratio of 5 in the southern half. The distribution is therefore similar to the continuum emission.
We perform a quick analysis to derive the gas column density of the disk by assuming a gas-to-dust ratio of 100 and a uniform Tex = 35 K (the brightness temperature, and physical temperature if optically thick, of 13C16O at the peak continuum emission) in the disk. We use the prescribed dust opacity by Beckwith et al. 1990, where the opacity is κ = 0.1(ν/1012 Hz)β cm2 g−1. A certain degree of grain growth is expected in the disk, thus we let the spectral slope β to be unity. The resulting opacity is κ = 0.01 cm2 g−1 at 99.5 GHz. We derived the gas column density to be 21 g cm−2 and 0.3 g cm−2 at the location of the maximum and the minimum peak intensity, respectively. However, we understand that since the dust is most likely to sediment at the disk midplane and the gas-to-dust ratio may vary across the disk, estimation of the gas mass can be improved by using the results of CO molecular lines, which will be discussed in the presentation.
The dust disk is observed to be divided into two parts, an inner disk and an outer disk, by a dust-depleted region. While the former is not resolved by the beam, the outer disk is detected out to a radius of 2 arcsec from the central star, and depending on the position angle its inner radius ranges from 0.5 arcsec to 1 arcsec. HD 142527 is known for its crescent-like outer disk in the millimeter and longer wavelengths, and our observation reveal the same non-axisymmetric features, where the disk northern region is brighter than the southern region. The peak intensity of the outer disk, as a function of position angle P.A. and radius r, shows a maximum of 11.5 mJy beam−1 at P.A. = 10°, r = 1.1 arcsec, and a minimum of 0.2 mJy beam−1 at P.A. = 237°, r = 1.3 arcsec; the contrast in intensity is thus about 60 between the two direction. The gas spatial distribution traced by 13C16O J = 1 − 0 line emission resembles that of the J = 3 − 2 of the same molecule; its integrated intensity is more axisymmetric and does not differ by more than a factor of two in the azimuthal direction.In addition, 13C16O is most probably optically thick as its brightness temperature is as high as 40 K even at 1 arcsec from the star. On the other hand, the distribution of the 12C18O J = 1 − 0 integrated intensity, unlike its J = 3 − 2 counterpart which shows an axisymmetric distribution around the central star, departs substantially from the azimuthal symmetry; its emission concentrates in the northern part of the disk that is about 25 K in brightness temperature, with almost no appreciable detection above a signal-to-noise ratio of 5 in the southern half. The distribution is therefore similar to the continuum emission.
We perform a quick analysis to derive the gas column density of the disk by assuming a gas-to-dust ratio of 100 and a uniform Tex = 35 K (the brightness temperature, and physical temperature if optically thick, of 13C16O at the peak continuum emission) in the disk. We use the prescribed dust opacity by Beckwith et al. 1990, where the opacity is κ = 0.1(ν/1012 Hz)β cm2 g−1. A certain degree of grain growth is expected in the disk, thus we let the spectral slope β to be unity. The resulting opacity is κ = 0.01 cm2 g−1 at 99.5 GHz. We derived the gas column density to be 21 g cm−2 and 0.3 g cm−2 at the location of the maximum and the minimum peak intensity, respectively. However, we understand that since the dust is most likely to sediment at the disk midplane and the gas-to-dust ratio may vary across the disk, estimation of the gas mass can be improved by using the results of CO molecular lines, which will be discussed in the presentation.