ABSTRACT
A woofer-tweeter deformable mirror (DM) driven by combined actuators with a piezoelectric unimorph and stack for astronomical applications is proposed. The piezoelectric unimorph "tweeter" part, made of a 200-µm-thick lead zirconate titanate film and 200-µm-thick silicon, has 234 separate elements for high-order correction. It is magnetically jointed with a seven-element "woofer" piezo-stack array, which is for low-order correction. The combined DM was fabricated and experimentally evaluated, showing a high resonant frequency near 1 kHz. The piezo-stack array together with the unimorph actuators enable the DM to produce wavefronts with RMS residue errors less than 20 nm. Experimental results indicate that the woofer-tweeter DM has the capability to compensate for the first 35 terms of Zernike aberrations with normalized RMS wavefront errors less than 20%. The woofer-tweeter DM has higher bandwidth than a conventional unimorph DM as well as simple structure, low cost, and good scalability, offering a potential alternative for large-aperture astronomical applications.
ABSTRACT
The LIGO detection of gravitational waves (GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes (AST3), located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source (GW 170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the i-band magnitude declining from 17.23±0.13 magnitude to 17.72±0.09 magnitude in ~1.8â¯h. The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about â¼10-2 solar mass of radioactive material at a speed of up to 30% the speed of light.
