The Complex Interstellar Na I Absorption toward h and Chi Persei

Abstract

Recent high spatial and spectral resolution investigations of the diffuse interstellar medium (ISM) have found significant evidence for small-scale variations in the interstellar gas on scales less than or equal to 1 pc. To better understand the nature of small-scale variations in the ISM, we have used the KPNO WIYN Hydra multi-object spectrograph, which has a mapping advantage over the single-axis, single-scale limitations of studies using high proper motion stars and binary stars, to obtain moderate resolution (~12 km/s) interstellar Na I D absorption spectra of 172 stars toward the double open cluster h and Chi Persei. All of the sightlines toward the 150 stars with spectra that reveal absorption from the Perseus spiral arm show different interstellar Na I D absorption profiles in the Perseus arm gas. Additionally, we have utilized the KPNO Coude Feed spectrograph to obtain high-resolution (~3 km/s) interstellar Na I D absorption spectra of 24 of the brighter stars toward h and Chi Per. These spectra reveal an even greater complexity in the interstellar Na I D absorption in the Perseus arm gas and show individual components changing in number, velocity, and strength from sightline to sightline. If each of these individual velocity components represents an isolated cloud, then it would appear that the ISM of the Perseus arm gas consists of many small clouds. Although the absorption profiles vary even on the smallest scales probed by these high-resolution data (~30";~0.35pc), our analysis reveals that some interstellar Na I D absorption components from sightline to sightline are related, implying that the ISM toward h and Chi Per is probably comprised of sheets of gas in which we detect variations due to differences in the local physical conditions of the gas.

27 pages text; 8 figures

References in corpus (15)

• The Star Formation History and Mass Function of the Double Cluster h and Chi Persei
• New Regime of MHD Turbulence: Cascade Below Viscous Cutoff
• The Small-scale Structure in Interstellar HI: A Resolvable Puzzle
• Formation and loss of hierarchical structure in two-dimensional MHD simulations of wave-driven turbulence in interstellar clouds
• The Structure of the Cold Neutral ISM on 10-100 Astronomical Unit Scales
• Small-Scale Interstellar Na I Structure Toward M92
• Small scale structure in molecular gas from multi-epoch observations of HD 34078
• Multi-epoch HI line measurements of 4 southern pulsars
• Variable Interstellar Absorption toward the Halo Star HD 219188 - Implications for Small-Scale Interstellar Structure
• Observations of Small Scale ISM Structure in Dense Atomic Gas
• Variable NaI Absorption toward rho Leo : Biased Neutral Formation in the Diffuse Interstellar Medium?
• Density Variations over Subparsec Scales in Diffuse Molecular Gas
• The Physical Characteristics of the Small-Scale Interstellar Structure towards Mu Crucis
• Does tiny-scale atomic structure exist in the interstellar medium ?
• Optical spectroscopy of the M15 intermediate velocity cloud

Cited by in corpus (13)

• Detailed maps of interstellar clouds in front of omega Centauri: Small-scale structures in the Galactic Disc-Halo interface
• Atomic and Ionized Microstructures in the Diffuse Interstellar Medium
• Tiny HI Clouds in the Local ISM
• Small-scale structure of the interstellar medium towards rho Oph stars: diffuse band observations
• Monitoring the Variable Interstellar Absorption toward HD 219188 with HST/STIS
• Spatial and Temporal Variations in Interstellar Absorption toward HD 72127AB
• The GALAH survey: New diffuse interstellar bands found in residuals of 872,000 stellar spectra
• Large and small-scale structure of the Intermediate and High Velocity Clouds towards the LMC and SMC
• Tiny HI Clouds in the Local ISM
• Dust properties along anomalous extinction sightlines. II. Studying extinction curves with dust models
• Temporal Variability of Interstellar Na I Absorption Toward The Monoceros Loop
• Spectroscopic and photometric time series of the bright RRc star T Sex
• The Advantage of Increased Resolution in the Study of Quasar Absorption Systems