Sonic boom simulation by means of low-pressure sources

Sonic boom simulation by low pressure source

Multi-level study of C3H2: The first interstellar hydrocarbon ring

Cyclic species in the interstellar medium have been searched for almost since the first detection of interstellar polyatomic molecules. Eleven different C3H2 rotational transitions were detected; 9 of which were studied in TMC-1, a nearby dark dust cloud, are shown. The 1 sub 10 yields 1 sub 01 and 2 sub 20 yields 2 sub 11 transitions were observed with the 43 m NRAO telescope, while the remaining transitions were detected with the 14 m antenna of the Five College Radio Observatory (FCRAO). The lines detected in TMC-1 have energies above the ground state ranging from 0.9 to 17.1 K and consist of both ortho and para species. Limited maps were made along the ridge for several of the transitions. The HC3N J = 2 yields 1 transition were mapped simultaneously with the C3H2 1 sub 10 yields 1 sub 01 line and therefore can compare the distribution of this ring with a carbon chain in TMC-1. C3H2 is distributed along a narrow ridge with a SE - NW extension which is slightly more extended than the HC2N J = 2 yields 1. Gaussian fits gives a FWHP extension of 8'5 for C3H2 while HC3N has a FWHP of 7'. The data show variations of the two velocity components along the ridge as a function of transition. Most of the transitions show a peak at the position of strongest HC3N emission while the 2 sub 21 yields 2 sub 10 transition shows a peak at the NH3 position

Thermally Activated Magnetization and Resistance Decay during Near Ambient Temperature Aging of Co Nanoflakes in a Confining Semi-metallic Environment

We report the observation of magnetic and resistive aging in a self assembled nanoparticle system produced in a multilayer Co/Sb sandwich. The aging decays are characterized by an initial slow decay followed by a more rapid decay in both the magnetization and resistance. The decays are large accounting for almost 70% of the magnetization and almost 40% of the resistance for samples deposited at 35 $^oC$. For samples deposited at 50 $^oC$ the magnetization decay accounts for $\sim 50$ of the magnetization and 50% of the resistance. During the more rapid part of the decay, the concavity of the slope of the decay changes sign and this inflection point can be used to provide a characteristic time. The characteristic time is strongly and systematically temperature dependent, ranging from $\sim1$x$10^2 s$ at 400K to $\sim3$x$10^5 s$ at 320K in samples deposited at $35 ^oC$. Samples deposited at 50 $^oC$ displayed a 7-8 fold increase in the characteristic time (compared to the $35 ^oC$ samples) for a given aging temperature, indicating that this timescale may be tunable. Both the temperature scale and time scales are in potentially useful regimes. Pre-Aging, Scanning Tunneling Microscopy (STM) reveals that the Co forms in nanoscale flakes. During aging the nanoflakes melt and migrate into each other in an anisotropic fashion forming elongated Co nanowires. This aging behavior occurs within a confined environment of the enveloping Sb layers. The relationship between the characteristic time and aging temperature fits an Arrhenius law indicating activated dynamics

The effects of star formation on the low-metallicity ISM: NGC4214 mapped with Herschel/PACS spectroscopy

We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214 observed in 6 far infrared fine-structure lines: [C II] 158mu, [O III] 88mu, [O I] 63mu, [O I] 146mu, [N II] 122mu, and [N II] 205mu. The maps are sampled to the full telescope spatial resolution and reveal unprecedented detail on ~ 150 pc size scales. We detect [C II] emission over the whole mapped area, [O III] being the most luminous FIR line. The ratio of [O III]/[C II] peaks at about 2 toward the sites of massive star formation, higher than ratios seen in dusty starburst galaxies. The [C II]/CO ratios are 20 000 to 70 000 toward the 2 massive clusters, which are at least an order of magnitude larger than spiral or dusty starbursts, and cannot be reconciled with single-slab PDR models. Toward the 2 massive star-forming regions, we find that L[CII] is 0.5 to 0.8% of the LTIR . All of the lines together contribute up to 2% of LTIR . These extreme findings are a consequence of the lower metallicity and young, massive-star formation commonly found in dwarf galaxies. These conditions promote large-scale photodissociation into the molecular reservoir, which is evident in the FIR line ratios. This illustrates the necessity to move to multiphase models applicable to star-forming clusters or galaxies as a whole.Comment: Accepted for publication in the A&A Herschel Special Issu

Star Formation in M51 Triggered by Galaxy Interaction

We have mapped the inner 360'' regions of M51 in the 158micron [CII] line at 55'' spatial resolution using the Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO). The emission is peaked at the nucleus, but is detectable over the entire region mapped, which covers much of the optical disk of the galaxy. There are also two strong secondary peaks at ~43% to 70% of the nuclear value located roughly 120'' to the north-east, and south-west of the nucleus. These secondary peaks are at the same distance from the nucleus as the corotation radius of the density wave pattern. The density wave also terminates at this location, and the outlying spiral structure is attributed to material clumping due to the interaction between M51 and NGC5195. This orbit crowding results in cloud-cloud collisions, stimulating star formation, that we see as enhanced [CII] line emission. The [CII] emission at the peaks originates mainly from photodissociation regions (PDRs) formed on the surfaces of molecular clouds that are exposed to OB starlight, so that these [CII] peaks trace star formation peaks in M51. The total mass of [CII] emitting photodissociated gas is ~2.6x10^{8} M_{sun}, or about 2% of the molecular gas as estimated from its CO(1-0) line emission. At the peak [CII] positions, the PDR gas mass to total gas mass fraction is somewhat higher, 3-17%, and at the secondary peaks the mass fraction of the [CII] emitting photodissociated gas can be as high as 72% of the molecular mass.... (continued)Comment: 14 pages, 6 figures, Accepted in ApJ (for higher resolution figures contact the author