Characterization of laser Doppler vibrometers using acousto-optic modulators

We report on a new approach to characterize the performance of a laser Doppler vibrometer (LDV). The method uses two acousto-optic modulators (AOMs) to frequency shift the light from an LDV by a known quantity to create a synthetic velocity shift that is traceable to a frequency reference. Results are presented for discrete velocity shifts and for sinusoidal velocity shifts that would be equivalent to what would be observed in an ideal accelerometer vibration calibration. The method also enables the user to sweep the synthetic vibration excitation frequency to characterize the bandwidth of an LDV together with its associated electronics.

Detailed Studies of IPHAS sources. II. Sab 19, a true planetary nebula and its mimic crossing the Perseus Arm.

The INT Photometric Hα Survey (IPHAS) has provided us with a number of new-emission line sources, among which planetary nebulae (PNe) constitute an important fraction. Here we present a detailed analysis of the IPHAS nebula Sab 19 (IPHASX J055242.8+262116) based on radio, infrared, and optical images and intermediate- and high-dispersion longslit spectra. Sab 19 consists of a roundish 0.10 pc in radius double-shell nebula surrounded by a much larger 2.8 pc in radius external shell with a prominent H-shaped filament. We confirm the nature of the main nebula as a PN whose sub-solar N/O ratio abundances, low ionized mass, peculiar radial velocity, and low-mass central star allow us to catalog it as a type III PN. Apparently, the progenitor star of Sab 19 became a PN when crossing the Perseus Arm during a brief visit of a few Myr. The higher N/O ratio and velocity shift ≃40 km s−1 of the external shell with respect to the main nebula and its large ionized mass suggest that it is not truly associated with Sab 19, but it is rather dominated by a Strömgren zone in the interstellar medium ionized by the PN central star.

Velocity shift of Mg ii and Al iii broad absorption lines in quasar SDSS J134444.33+315007.6

ABSTRACT We report, for the first time, a synchronized velocity shift of Mg ii and Al iii broad absorption lines (BALs) in quasar SDSS J134444.33+315007.6 (hereafter, J1344+3150). We found this quasar from a sample of 134 Mg ii BAL quasars with multi-epoch observations. This quasar contains three low-ionization BAL systems, the fastest of which at ${\sim} -17\, 000\, \rm km\, s^{-1}$ shows a kinematic shift of ${\sim} -1101$ and $\sim -1170\, \rm km\, s^{-1}$ in its Mg ii and Al iii ions, respectively, during a rest-frame time of about 3.21 yr. Meanwhile, this quasar also shows other various variation characteristics, including an obvious weakening in its continuum, a coordinated enhancement in multiple emission lines (Mg ii, C iii, and Al iii), and a coordinated enhancement in three Al iii absorption troughs. These variation characteristics convincingly indicate that the BAL outflows of J1344+3150 are under the influence from the background radiation energy. Thus, we infer that the velocity shift displayed in system A in the quasar J1344+3150 may indicate an actual line-of-sight acceleration of an outflow due to the radiation pressure from the central source.

Detection of Na, K, and Hα absorption in the atmosphere of WASP-52b using ESPRESSO

WASP-52b is a low-density hot Jupiter orbiting a moderately active K2V star. Previous low-resolution studies have revealed a cloudy atmosphere and found atomic Na above the cloud deck. Here we report on the detection of excess absorption at the Na doublet, the Hα line, and the K D1 line. We derived a high-resolution transmission spectrum based on three transits of WASP-52b, observed with the ultra-stable, high-resolution spectrograph ESPRESSO at the Very Large Telescope array. We measured a line contrast of 1.09 ± 0.16% for Na D1, 1.31 ± 0.13% for Na D2, 0.86 ± 0.13% for Hα, and 0.46 ± 0.13% for K D1, with a line FWHM range of 11–22 km s−1. We also found that the velocity shift of these detected lines during the transit is consistent with the planet’s orbital motion, thus confirming their planetary origin. We did not observe any significant net blueshift or redshift that could be attributed to planetary winds. We used activity indicator lines as control but found no excess absorption. However, we did notice signatures arising from the Center-to-Limb variation (CLV) and the Rossiter-McLaughlin (RM) effect at these control lines. This highlights the importance of the CLV + RM correction in correctly deriving the transmission spectrum, which, if not corrected, could resemble or cancel out planetary absorption in certain cases. WASP-52b is the second non-ultra-hot Jupiter to show excess Hα absorption after HD 189733b. Future observations targeting non-ultra-hot Jupiters that show Hα could help reveal the relation between stellar activity and the heating processes in the planetary upper atmosphere.

The MUSE Hubble Ultra Deep Field Survey

We present spatially resolved maps of six individually-detected Lyman α haloes (LAHs) as well as a first statistical analysis of the Lyman α (Lyα) spectral signature in the circum-galactic medium of high-redshift star-forming galaxies (−17.5 > MUV > −21.5) using the Multi-Unit Spectroscopic Explorer. Our resolved spectroscopic analysis of the LAHs reveals significant intrahalo variations of the Lyα line profile. Using a three-dimensional two-component model for the Lyα emission, we measured the full width at half maximum (FWHM), the peak velocity shift, and the asymmetry of the Lyα line in the core and in the halo of 19 galaxies. We find that the Lyα line shape is statistically different in the halo compared to the core (in terms of width, peak wavelength, and asymmetry) for ≈40% of our galaxies. Similarly to object-by-object based studies and a recent resolved study using lensing, we find a correlation between the peak velocity shift and the width of the Lyα line both at the interstellar and circum-galactic scales. This trend has been predicted by radiative transfer simulations of galactic winds as a result of resonant scattering in outflows. While there is a lack of correlation between the spectral properties and the spatial scale lengths of our LAHs, we find a correlation between the width of the line in the LAH and the halo flux fraction. Interestingly, UV bright galaxies (MUV < −20) show broader, more redshifted, and less asymmetric Lyα lines in their haloes. The most significant correlation found is for the FWHM of the line and the UV continuum slope of the galaxy, suggesting that the redder galaxies have broader Lyα lines. The generally broad and red line shapes found in the halo component suggest that the Lyα haloes are powered either by scattering processes through an outflowing medium, fluorescent emission from outflowing cold clumps of gas, or a mix of both. Considering the large diversity of the Lyα line profiles observed in our sample and the lack of strong correlation, the interpretation of our results is still broadly open and underlines the need for realistic spatially resolved models of the LAHs.

MusE GAs FLOw and Wind (MEGAFLOW) IV. A two sightline tomography of a galactic wind

ABSTRACT Galactic outflows are thought to eject baryons back out to the circumgalactic medium. Studies based on metal absorption lines (Mg ii in particular) in the spectra of background quasars indicate that the gas is ejected anisotropically, with galactic winds likely leaving the host in a bi-conical flow perpendicular to the galaxy disc. In this paper, we present a detailed analysis of an outflow from a z = 0.7 ‘green-valley’ galaxy [log (M*/M⊙) = 9.8; $\mbox{SFR}=0.5\, \mathrm{M}_{\odot }\, \mathrm{yr}^{-1}$] probed by two background sources from the MusE GAs FLOw and Wind (MEGAFLOW) survey. Thanks to a fortuitous configuration with a background quasar (SDSSJ1358 + 1145) and a bright background galaxy at z = 1.4, both at impact parameters of $\approx\! 15\, \hbox{kpc}$, we can – for the first time – probe both the receding and approaching components of a putative galactic outflow around a distant galaxy. We measure a significant velocity shift between the Mg ii absorption from the two sightlines ($84\pm 17\, \hbox{km~s$^{-1}$}$), which is consistent with the expectation from our simple fiducial wind model, possibly combined with an extended disc contribution.

FIESTA – disentangling stellar variability from exoplanets in the Fourier domain

ABSTRACT We propose a new analysis methodology – FourIEr phase SpecTrum Analysis (FIESTA, or $\mathit {\Phi }$ESTA) – for the study of spectral line profile variability in Fourier space. The philosophy of $\mathit {\Phi }$ESTA is highlighted in its interpretation of a line deformation as various shifts of the composing Fourier modes. With this ability, $\mathit {\Phi }$ESTA excels in distinguishing the effects of a bulk shift in a line profile, from changes in a line profile shape. In other words, it can distinguish a radial velocity shift due to orbiting companions like planets, from an apparent radial velocity shift due to stellar variability (often referred to as ‘jitter’). Most importantly, it can quantify the radial velocity impact of stellar jitter on each epoch. Our simulations show that (compared to a model that does not account for stellar activity), $\mathit {\Phi }$ESTA can almost triple the fraction of planets recovered with orbital parameters measured to within 10 per cent of their input parameters, when extracting a 2 m s−1 amplitude planetary signal in the midst of ∼2 m s−1 amplitude starspot jitter for high signal-to-noise ratio (&gt;200 pixel−1) data. $\mathit {\Phi }$ESTA can also be used to identify stellar activity related periods in a periodogram analysis and classify relative amplitudes of stellar jitter and planetary signals, with examples for the analysis of HARPS data of the active star HD 224789 and the active planet-host star HD 103720. In the end, we demonstrate that $\mathit {\Phi }$ESTA’s framework is working as well as other activity indicators in correlating with stellar jitter.

Characterization of drag reduction performance over rotating microgrooves with different cross-sections

This paper presents a study of cross-sectional parameters and optimal drag reduction performance specifically for drag reduction in rotating microgroove applications. Rotating triangular microgrooves with nine asymmetrical and symmetrical cross-sections were numerically studied. In addition, a representative symmetrical rotating microgroove was experimentally tested. Positive asymmetrical microgrooves (including symmetrical microgrooves) were found to be sensitive to rotating Reynolds numbers and produced more significant drag reduction. Compared with a dimensioned asymmetry variable and other dimensionless parameters, the dimensionless asymmetry variable i+ could be used to describe drag reduction performance, which captured both the influence of microgroove cross-sectional asymmetry and turbulence intensity. A maximum drag reduction of up to 8.9% was obtained at 9.2 i+. With the exception of the torque, the velocity shift obtained from dimensionless velocity profiles could also be used to predict drag reduction performance, which has the potential for wider and more comprehensive application for any drag reduction technology.