We present a multiplicity census for a volume-complete all-sky survey of 422 stars with distances less than 25 pc and primary main-sequence effective temperatures T eff ≥ 5300 K. Very similar to previous results that have been presented for various subsets of this survey, we confirm the positive correlation of the stellar multiplicities with primary mass. We find for the F- and G-type Population I stars that 58% are non-single and 21% are in triple or higher level systems. For the old intermediate-disk and Population II stars—virtually all of G type and less massive—even two out of three sources prove to be non-single. These numbers being lower limits because of the continuous flow of new discoveries, the unbiased survey clearly demonstrates that the standard case for solar-type field stars is a hydrogen-burning source with at least one ordinary or degenerate stellar companion, and a surprisingly large number of stars are organized in multiple systems. A principal consequence is that orbital evolution, including the formation of blue straggler stars, is a potentially important issue on all spatial scales and timescales for a significant percentage of the stellar systems, in particular among Population II stars. We discuss a number of recent observations of known or suspected companions in the local survey, including a new detection of a double-lined Ba-Bb subsystem to the visual binary HR 8635.

Aims. We investigate the surroundings of the hypercompact H ii region M 17 UC1 to probe the physical properties of the associated young stellar objects and the environment of massive star formation. Methods. We use diffraction-limited near-IR (VLT/NACO) and mid-IR (VLT/VISIR) images to reveal the different morphologies at various wavelengths. Likewise, we investigate the stellar and nebular content of the region with VLT/SINFONI integral field spectroscopy with a resolution R ∼ 1500 at H + K bands. Results. Five of the seven point sources in this region show L-band excess emission. A geometric match is found between the H 2 emission and near-IR polarized light in the vicinity of IRS5A, and between the diffuse mid-IR emission and near-IR polarization north of UC1. The H 2 emission is typical for dense photodissociation regions (PDRs), which are initially far-ultraviolet pumped and repopulated by collisional de-excitation. The spectral types of IRS5A and B273A are B3−B7 V/III and G4−G5 III, respectively. The observed infrared luminosity L IR in the range 1−20 μm is derived for three objects; we obtain 2.0 × 10 3 L for IRS5A, 13 L for IRS5C, and 10 L for B273A. Conclusions. IRS5 might be a young quadruple system. Its primary star IRS5A is confirmed to be a high-mass protostellar object (∼9 M , ∼1 × 10 5 yrs); it might have terminated accretion due to the feedback from stellar activities (radiation pressure, outflow) and the expanding H ii region of M 17. The object UC1 might also have terminated accretion because of the expanding hypercompact H ii region, which it ionizes. The disk clearing process of the low-mass young stellar objects in this region might be accelerated by the expanding H ii region. The outflows driven by UC1 are running south-north with its northeastern side suppressed by the expanding ionization front of M 17; the blue-shifted outflow lobe of IRS5A is seen in two types of tracers along the same line of sight in the form of H 2 emission filament and mid-emission. The H 2 line ratios probe the properties of M 17 SW PDR, which is confirmed to have a clumpy structure with two temperature distributions: warm, dense molecular clumps with n H > 10 5 cm −3 and T ≈ 575 K and cooler atomic gas with n H ∼ 3.7 × 10 3 −1.5 × 10 4 cm −3 and T ∼ 50−200 K.

We report the detection of a curved magnetic field in the ring-like shell of the bubble N4, derived from near-infrared polarization of reddened diskless stars located behind this bubble. The magnetic field in the shell is curved and parallel to the ring-like shell, and its strength is estimated to be ∼ 120 µG in the plane of the sky. The magnetic field strength in the shell is significantly enhanced compared to the local field strength. We calculate the mass-to-flux ratio for the submillimeter clumps in the shell and find that they are all magnetically subcritical. Our results demonstrate that the magnetic field strengthens as the interstellar medium is compressed into a shell, and suggest that the magnetic field has the potential to hinder star formation triggered by H II region expansion.