Stacking Spectra in Protoplanetary Disks: Detecting Intensity Profiles from Hidden Molecular Lines in HD 163296

Abstract

We introduce a new stacking method in Keplerian disks that (1) enhances signal-to-noise ratios (S/N) of detected molecular lines and (2) that makes visible otherwise undetectable weak lines. Our technique takes advantage of the Keplerian rotational velocity pattern. It aligns spectra according to their different centroid velocities at their different positions in a disk and stacks them. After aligning, the signals are accumulated in a narrower velocity range as compared to the original line width without alignment. Moreover, originally correlated noise becomes de-correlated. Stacked and aligned spectra, thus, have a higher S/N. We apply our method to ALMA archival data of DCN (3-2), DCO+ (3-2), N2D+ (3-2), and H2CO (3_0,3-2_0,2), (3_2,2-2_2,1), and (3_2,1-2_2,0) in the protoplanetary disk around HD 163296. As a result, (1) the S/N of the originally detected DCN (3-2), DCO+ (3-2), and H2CO (3_0,3-2_0,2) and N2D+ (3-2) lines are boosted by a factor of >4-5 at their spectral peaks, implying one order of magnitude shorter integration times to reach the original S/N; and (2) the previously undetectable spectra of the H2CO (3_2,2-2_2,1) and (3_2,1-2_2,0) lines are materialized at more than 3 sigma. These dramatically enhanced S/N allow us to measure intensity distributions in all lines with high significance. The principle of our method can not only be applied to Keplerian disks but also to any systems with ordered kinematic patterns.

9 pages, 5 figures, accepted by ApJ, comment welcome

References in corpus (3)

• Gas and Dust Emission at the Outer Edge of Protoplanetary Disks
• Millimeter imaging of HD 163296: probing the disk structure and kinematics
• CO mass upper limits in the Fomalhaut ring - the importance of NLTE excitation in debris discs and future prospects with ALMA

Cited by in corpus (7)

• A Three-Dimensional View of Turbulence: Constraints on Turbulent Motions in the HD 163296 Protoplanetary Disk using DCO${}^{+}$
• Different dust and gas radial extents in protoplanetary disks: consistent models of grain growth and CO emission
• An ALMA survey of DCN/H${}^{13}$CN and DCO${}^{+}$/H${}^{13}$CO${}^{+}$ in protoplanetary disks
• An ALMA Survey of H${}_2$CO in Protoplanetary Disks
• DCO${}^{+}$, DCN and N${}_2$D${}^{+}$ reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296
• Increased H${}_2$CO production in the outer disk around HD 163296
• Line Ratios Reveal N2H+ Emission Originates Above the Midplane in TW Hydrae