UV-Visual Echelle Spectrograph Research Articles

Tracking Outflow Using Line Locking (TOLL). I. The Case Study of Quasar J221531-174408

Investigating line-locked phenomena within quasars is crucial for understanding the dynamics of quasar outflows, the role of radiation pressure in astrophysical flows, and the star formation history and metallicity of the early Universe. We have initiated the Tracking Outflow by Line Locking project to study quasar outflow by studying line-locking signatures using high-resolution high-signal-to-noise-ratio quasar spectra. In this paper, we present a case study of the line-locking signatures from QSO J221531-174408. The spectrum was obtained using the Very Large Telescope’s UV Visual Echelle Spectrograph. We first identify associated absorbers in the spectrum using C iv, N v, and Si iv doublets and measure their velocity shifts, covering fractions, and column densities through a line-profile-fitting technique. Then we compare the velocity separations between different absorbers, and detect nine pairs of line-locked C iv doublets, three pairs of line-locked N v doublets, and one pair of line-locked Si iv doublets. This is one of the four quasars known to possess line-locked signatures in C iv, Si iv, and N v at the same time. We also find three complex line-locked systems, where three to five absorbers are locked together through multi-ion doublets. Our study suggests that line locking is a common phenomenon in the quasar outflows, and theoretical models involving more than two clouds and one ionic doublet are needed in the future to explain the formation of these complex line-locking signatures.

The Pristine survey – XVII. The C-19 stream is dynamically hot and more extended than previously thought

ABSTRACT The C-19 stream is the most metal-poor stellar system ever discovered, with a mean metallicity [Fe/H] = −3.38 ± 0.06. Its low metallicity dispersion (σ[Fe/H] < 0.18 at the 95 per cent confidence level) and variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use Very Large Telescope (VLT)/UV–Visual Echelle Spectrograph (UVES) spectra of seven C-19 stars to derive more precise velocity measurements for member stars, and to identify two new members with radial velocities and metallicities consistent with the stream’s properties. One of these new member stars is located 30° away from the previously identified body of C-19, implying that the stream is significantly more extended than previously known and that more members likely await discovery. In the main part of C-19, we measure a radial velocity dispersion σv = 6.2$^{+2.0}_{-1.4}{\rm \, km\, s^{-1}}$ from nine members, and a stream width of 0.56° ± 0.08°, equivalent to ∼158 pc at a heliocentric distance of 18 kpc. These confirm that C-19 is comparatively hotter, dynamically, than other known globular cluster streams and shares the properties of faint dwarf galaxy streams. On the other hand, the variations in the Na abundances of the three newly observed bright member stars, the variations in Mg and Al for two of them, and the normal Ba abundance of the one star where it can be measured provide further evidence for a globular cluster origin. The tension between the dynamical and chemical properties of C-19 suggests that its progenitor experienced a complex birth environment or disruption history.

An inventory of atomic species in the atmosphere of WASP-121b using UVES high-resolution spectroscopy

ABSTRACT Ultrahot Jupiters (UHJs) present excellent targets for atmospheric characterization. Their hot dayside temperatures (T ≳ 2200 K) strongly suppress the formation of condensates, leading to clear and highly inflated atmospheres extremely conducive to transmission spectroscopy. Recent studies using optical high-resolution spectra have discovered a plethora of neutral and ionized atomic species in UHJs, placing constraints on their atmospheric structure and composition. Our recent work has presented a search for molecular features and detection of Fe i in the UHJ WASP-121b using Very Large Telescope (VLT)/UV–Visual Echelle Spectrograph (UVES) transmission spectroscopy. Here, we present a systematic search for atomic species in its atmosphere using cross-correlation methods. In a single transit, we uncover potential signals of 17 atomic species that we investigate further, categorizing five as strong detections, three as tentative detections, and nine as weak signals worthy of further exploration. We confirm previous detections of Cr i, V i, Ca i, K i, and exospheric H i and Ca ii made with the High Accuracy Radial velocity Planet Searcher (HARPS) and the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), and independently re-recover our previous detection of Fe i at 8.8σ using both the blue and red arms of the UVES data. We also add a novel detection of Sc ii at 4.2σ. Our results further demonstrate the richness of UHJs for optical high-resolution spectroscopy.

Non-detection of TiO and VO in the atmosphere of WASP-121b using high-resolution spectroscopy

Thermal inversions have long been predicted to exist in the atmospheres of ultra-hot Jupiters. However, the detection of two species thought to be responsible – titanium oxide and vanadium oxide – remains elusive. We present a search for TiO and VO in the atmosphere of the ultra-hot Jupiter WASP-121b (Teq ≳ 2400 K), an exoplanet with evidence of VO in its atmosphere at low resolution which also exhibits water emission features in its dayside spectrum characteristic of a temperature inversion. We observed its transmission spectrum with the UV-Visual Echelle Spectrograph at the Very Large Telescope and used the cross-correlation method – a powerful tool for the unambiguous identification of the presence of atomic and molecular species – in an effort to detect whether TiO or VO were responsible for the observed temperature inversion. No evidence for the presence of TiO or VO was found at the terminator of WASP-121b. By injecting signals into our data at varying abundance levels, we set rough detection limits of [VO] ≲−7.9 and [TiO] ≲−9.3. However, these detection limits are largely degenerate with scattering properties and the position of the cloud deck. Our results may suggest that neither TiO or VO are the main drivers of the thermal inversion in WASP-121b; however, until a more accurate line list is developed for VO, we cannot conclusively rule out its presence. Future works will consist of a search for other strong optically-absorbing species that may be responsible for the excess absorption in the red-optical.

VLT/UVES observations of peculiarαabundances in a sub-DLA atz≈ 1.8 towards the quasar B1101−26

We present a detailed analysis of chemical abundances in a sub-damped Lyman alpha absorber at z=1.839 towards the quasar B1101-26, based on a very-high-resolution (R ~ 75,000) and high-signal-to-noise (S/N >100) spectrum observed with the UV Visual Echelle spectrograph (UVES) installed on the ESO Very Large Telescope (VLT). The absorption line profiles are resolved into a maximum of eleven velocity components spanning a rest-frame velocity range of 200 km/s. Detected ions include CII, CIV, NII, OI, MgI, MgII, AlII, AlIII, SiII, SiIII, SiIV, FeII, and possibly SII. The total neutral hydrogen column density is log N(HI) = 19.48 +/- 0.01. From measurements of column densities and Doppler parameters we estimate element abundances of the above-given elements. The overall metallicity, as traced by [OI/HI], is -1.56 +/- 0.01. For the nitrogen-to-oxygen ratio we derive an upper limit of [NI/OI] < -0.65, which suggests a chemically young absorption line system. This is supported by a supersolar alpha/Fe ratio of [SiII/FeII] ~ 0.5. The most striking feature in the observed abundance pattern is an unusually high sulphur-to-oxygen ratio of 0.69 < [SII/OI] < 1.26. We calculate detailed photoionisation models for two subcomponents with Cloudy, and can rule out that ionisation effects alone are responsible for the high S/O ratio. We instead speculate that the high S/O ratio is caused by the combination of several effects, such as specific ionisation conditions in multi-phase gas, unusual relative abundances of heavy elements, and/or dust depletion in a local gas environment that is not well mixed and/or that might be related to star-formation activity in the host galaxy. We discuss the implications of our findings for the interpretation of alpha-element abundances in metal absorbers at high redshift.

Mapping zonal winds at Venus’s cloud tops from ground-based Doppler velocimetry

The most significant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms. Here we report on ground-based Doppler velocimetry measurements of the zonal winds, based on high resolution spectra from the UV–Visual Echelle Spectrograph (UVES) instrument at ESO’s Very Large Telescope. Under the assumption of predominantly zonal flow, this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side. The technique, based on long slit spectroscopy combined with the high spatial resolution provided by the VLT, has provided the first ground-based characterization of the latitudinal profile of zonal wind in the atmosphere of Venus, the first zonal wind field map in the visible, as well as new constraints on wind variations with local time. We measured mean zonal wind amplitudes between 106±21 and 127±14m/s at latitudes between 18°N and 34°S, with the zonal wind being approximately uniform in 2.6°-wide latitude bands (0.3arcsec at disk center). The zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking, but with non-negligible variability in local time (longitude) and in latitude. Near 50° the presence of moderate jets is apparent in both hemispheres, with the southern jet being stronger by ∼10m/s. Small scale wind variations with local time are also present at low and mid-latitudes.

A new concept for the combination of optical interferometers and high-resolution spectrographs

The combination of high spatial and spectral resolution in optical astronomy enables new observational approaches to many open problems in stellar and circumstellar astrophysics. However, constructing a high-resolution spectrograph for an interferometer is a costly and time-intensive undertaking. Our aim is to show that, by coupling existing high-resolution spectrographs to existing interferometers, one could observe in the domain of high spectral and spatial resolution, and avoid the construction of a new complex and expensive instrument. We investigate in this article the different challenges which arise from combining an interferometer with a high-resolution spectrograph. The requirements for the different sub-systems are determined, with special attention given to the problems of fringe tracking and dispersion. A concept study for the combination of the VLTI (Very Large Telescope Interferometer) with UVES (UV-Visual Echelle Spectrograph) is carried out, and several other specific instrument pairings are discussed. We show that the proposed combination of an interferometer with a high-resolution spectrograph is indeed feasible with current technology, for a fraction of the cost of building a whole new spectrograph. The impact on the existing instruments and their ongoing programs would be minimal.

Stratification and isotope separation in CP stars

We investigate the elemental and isotopic stratification in the atmospheres of selected chemically peculiar (CP) stars of the upper main sequence. Reconfiguration of the UV-Visual Echelle Spectrograph in 2004 has made it possible to examine all three lines of the Ca II infrared (IR) triplet. Much of the material analysed was obtained in 2008. We support the claim of Ryabchikova, Kochukhov & Bagnulo (RKB) that the calcium isotopes have distinct stratification profiles for the stars 10 Aql, HR 1217 and HD 122970, with the heavy isotope concentrated towards the higher layers. Better observations are needed to learn the extent to which 40 Ca dominates in the deepest layers of all or most CP stars that show the presence of 48 Ca. There is little evidence for 40 Ca in the spectra of some HgMn stars, and the infrared (IR) triplet in the magnetic star HD 101065 is well fit by pure 48 Ca. In HR 5623 (HD 133792) and HD 217522, it is likely that the heavy isotope dominates, though models are possible where this is not the case. While elemental stratification is surely needed in many cases, we point out the importance of including adjustments in the assumed T eff and log (g) values, in attempts to model stratification. We recommend emphasis on profiles of the strongest lines, where the influence of stratification is most evident. Isotopic mixtures, involving the four stable calcium nuclides with masses between 40 and 48 are plausible, but are not emphasized.

A search for rapid pulsations in the magnetic cool chemically peculiar star HD 3980★

The Ap star HD 3980 appears to be a promising roAp candidate based on its fundamental parameters, leading us to search for rapid pulsations with the VLT UV-Visual Echelle Spectrograph (UVES). A precise Hipparcos parallax and estimated temperature of 8100 K place HD 3980 in the middle of the theoretical instability strip for rapidly oscillating Ap stars, about halfway through its main-sequence evolution stage. The star has a strong, variable magnetic field, as is typical of the cool magnetic Ap stars. Dipole model parameters were determined from VLT observations using Focal Reducer and low Dispersion Spectrograph (FORS)1. From Doppler shift measurements for individual spectral lines of rare-earth elements and the Hα line core, we find no pulsations above 20–30 m s−1. This result is corroborated by the inspection of lines of several other chemical elements, as well as with cross-correlation for long spectral regions with the average spectrum as a template. Abundances of chemical elements were determined and show larger than solar abundances of rare-earth elements. Further, ionization disequilibria for the first two ionized states of Nd and Pr are detected. We also find that the star has a strong overabundance of manganese, which is typical for much hotter HgMn and other Bp stars. Line profile variability with the rotation period was detected for the majority of chemical species.

HR 710 (HD 15144): an ultra-Sr-rich, magnetic Ap star with a close companion

The magnetic, chemically peculiar A-star HR 710 (HD 15144, ADS 1849A, AB Cet) has a close companion in a nearly circular orbit. Its 3-d period is unusually short for such stars. The system emits moderately hard X-rays, which likely come from a white dwarf secondary (ADS 1849Ab). The Sr ii spectrum is very strong, and the resonance lines show similar core-nib structure to the stronger Ca K line. We place only loose constraints on a model. There are indications of a lower electron/gas pressure than expected from the star's parallax and brightness. Strong-line profiles and anomalous excitation/ionization indicate significant deviations from traditional models, fixed by Teff, log g and abundances. Weak spectral-line profiles and wavelength shifts probably indicate abundance patches rather than the presence of a secondary (ADS 1849Ab) spectrum. Our UV–Visual Echelle Spectrograph (UVES) spectra are from only one epoch. Additional low-noise, high-resolution spectra are needed. We discuss the spectrum within the context of abundance stratification.

UVES radial velocity accuracy from asteroid observations

Context. High resolution observations of the asteroids Iris and Juno have been performed by means of the UV-Visual Echelle Spectrograph (UVES) at the European Southern Observatory (ESO) Very Large Telescope (VLT) to obtain the effective accuracy of the spectrograph’s radial velocity. The knowledge of this quantity has important bearings on studies searching for a variability in the fine structure constant carried out with this instrument. Aims. Asteroids provide a precise radial velocity reference at the level of 1 m s −1 , which allows for instrumental calibration and the recognition of small instrumental drifts and calibration systematics. In particular, radial velocity drifts due to nonuniform slit illumination and slit optical misalignment in the two UVES spectrograph arms can be investigated. Methods. We compare the position of the solar spectrum reflected by the asteroids with the solar wavelength positions and with that of asteroid and twilight observations at other epochs to asses the UVES instrumental accuracy. Results. We observe radial velocities offsets in the range of ≈10−50 m s −1 , likely due to a nonuniform slit illumination. However, no radial velocity patterns with wavelengths are detected and the two UVES arms provide consistent radial velocities. These results suggest that the detected ∆α/α variability by Levshakov et al. (2007) deduced from a drift of −180 ± 85 m s −1 at zabs = 1.84, between two sets of Feii lines falling in the two UVES arms, may be real or induced by other kinds of systematics than those investigated here. The proposed technique allows us to make a real time quality check of the spectrograph and should be followed for very accurate measurements.

Most precise single redshift bound to $\mathsf{\Delta\alpha/\alpha}$

Aims.Verification the theoretical prediction of oscillation of the fine-structure constant over cosmic time requires high precision measurements at individual redshifts. In earlier studies the mean values averaged over wide redshift intervals were usually reported. This requirement can be met using the single ion differential α measurement (SIDAM) procedure. We apply SIDAM to the lines associated with the damped Lyα system observed at zabs = 1.15 in the spectrum of HE 0515–4414. Methods.The spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). Results.The weighted mean calculated using carefully selected 34 pairs (, and 2586 Å) is ( C.L.). The precision of this estimate improves by a factor of 2 the previous one reported for the same system. The obtained result represents an absolute improvement with respect to what has been done in the measurements of .

VLT/UVES constraints on the carbon isotope ratio $^\mathsf{12}$C/$^\mathsf{13}$C at z = 1.15 toward the quasar HE 0515–4414

Aims. We analyzed the C I lines associated with the damped Lya system observed at z abs = 1.15 in the spectrum of HE 0515-4414 to derive the 12 C/ 13 C ratio. Methods. The spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). Results. The obtained lower limit 12 C/ 13 C > 80 (2σ C.L.) shows for the first time that the abundance of 13 C in the extragalactic intervening clouds is very low. This rules out a significant contribution from intermediate-mass stars to the chemical evolution of matter sampled by this line of sight. The estimated low amount of 13 C is in agreement with low abundances of nitrogen observed in damped Lya systems - the element produced in the same nuclear cycles and from about the same stars as 13 C.

Characterization of zonal winds in the stratosphere of Titan with UVES

Titan has been observed with UVES, the UV–Visual Echelle Spectrograph at the Very Large Telescope, with the aim of characterizing the zonal wind flow. We use a retrieval scheme originally developed for absolute stellar accelerometry [Connes, P., 1985. Astrophys. Space Sci., 110, 211–255] to extract the velocity signal by simultaneously taking into account all the lines present in the spectrum. The method allows to measure the Doppler shift induced at a given point by the zonal wind flow, with high precision. The short-wavelength channel (4200–5200 Å) probes one scale height higher than the long-wavelength one (5200–6200 Å), and we observe statistically significant evidence for stronger winds at higher altitudes. The results show a high dispersion. Globally, we detect prograde zonal winds, with lower limits of 62 and 50 m s −1 at the regions centered at 200 and 170 km altitude, but approximately a quarter of the measurements indicates null or retrograde winds.

Metal Abundances in a Damped Lyα System along Two Lines of Sight atz= 0.93

We study metal abundances in the z = 0.9313 damped Lyα system observed along the two lines of sight, A and B, toward the gravitationally lensed double QSO HE 0512-3329. Spatially resolved Space Telescope Imaging Spectrograph spectra constrain the neutral-gas column density to be N(H ) = 1020.5 cm-2 in both A and B. UV-visual Echelle Spectrograph spectra (spectral resolution FWHM = 9.8 km s-1) show, in contrast, significant line-of-sight differences in the column densities of Mn II and Fe II; these are not due to observational systematics. We find that [Mn/H] = -1.44 and [Fe/H] = -1.52 in damped Lyα system A, while [Mn/H] = -0.98 and [Fe/H] > -1.32, and possibly as high as [Fe/H] ≈ -1, in damped Lyα system B. A careful assessment of possible systematic errors leads us to conclude that these transverse differences are significant at a 5 σ level or greater. Although nucleosynthesis effects may also be at play, we favor differential dust depletion as the main mechanism producing the observed abundance gradient. The transverse separation is 5 h kpc at the redshift of the absorber, which is also likely to be the lensing galaxy. The derived abundances therefore probe two opposite sides of a single galaxy hosting both damped Lyα systems. This is the first time firm abundance constraints have been obtained for a single damped system probed by two lines of sight. The significance of this finding for the cosmic evolution of metals is discussed.

VLT/UVES constraints on the cosmological variability of the fine-structure constant

We propose a new methodology for probing the cosmological variability of α from pairs of Fe  lines (SIDAM, single ion differential α measurement) observed in individual exposures from a high resolution spectrograph. By this we avoid the influence of the spectral shifts due to (i) ionization inhomogeneities in the absorbers; and (ii) non-zero offsets between different exposures. Applied to the Fe  lines of the metal absorption line system at zabs = 1.839 in the spectrum of Q 1101-264 obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT), SIDAM provides ∆α/α = (2.4 ± 3.8stat) × 10 −6 .T hezabs = 1.15 Fe  system toward HE 0515-4414 has been re-analyzed by this method thus obtaining for the combined sample ∆α/α = (0.4 ± 1.5stat) × 10 −6 . These values are shifted with respect to the Keck/HIRES mean ∆α/α = (−5.7 ± 1.1stat) × 10 −6 (Murphy et al. 2004) at very high confidence level (95%). The fundamental photon noise limitation in the ∆α/α measurement with the VLT/UVES is discussed to figure the prospects for future observations. It is suggested that with a spectrograph of ∼10 times the UVES dispersion coupled to a 100 m class telescope the present Oklo level (∆α/α ≥ 4.5 × 10 −8 )

High-resolution spectroscopy of flat-spectrum quasars

We report Very Large Telescope (VLT) observations of the quasar PKS 2145+067. We obtained high-resolution (R ≈ 100 000 or 3 km s −1 ) optical spectra with the UV-Visual Echelle Spectrograph (UVES) at the VLT UT2 telescope. The emission redshift measured from (O  )i szem = 1.0003. In our spectra, the well-known intervening metal-rich absorption system at zabs = 0.79089 shows Mg  absorption lines resolved into 15 velocity components with a total spread of about 206 km s −1 . This absorption is consistent with a line of sight passing through the extended gaseous halo of a disk galaxy. The derived Doppler line broadening parameters are in the range b = 2t o 5k m s −1 . We also detected absorption lines of Mg  ,F e ,a nd Ca in the same system. The ionization state of the absorbing gas is analyzed and compared with previous studies of PKS 2145+067. Finally, we discuss the implications of high-resolution data for proposed cosmological variations of the fine-structure constant.

Chemical composition and evolutionary status of nine UV-bright stars in five globular clusters from VLT/UVES spectra

We have derived the chemical composition of nine UV-bright stars belonging to five Galactic globular clusters of various metallicities ((Fe/H) from −1. 0t o−2.4 dex). The analyses are based on high resolution spectra obtained with the UV-Visual Echelle Spectrograph (UVES) at VLT-UT2. The evolutionary status of the stars is assessed from the chemical anal- ysis and location in the H-R diagram. The star ID7 in NGC 5986 is confirmed as a bona fide post-asymptotic giant branch star (post-AGB) whereas the high- luminosity star ID6 has probably left the AGB before the third dredge-up. ZNG 1 in NGC 6712 shows an overabundance of sodium, oxygen, and silicon similar to overabundances we find in the UV-bright star ID6 in NGC 5986; both stars could be in a post-early-AGB (PEAGB) phase of evolution. The UV-bright star ZNG 7 in NGC 6218 seems to be an AGB star. The stars V-4 and ZNG 5 in NGC 6656 are in a post-horizontal-branch phase of evolution, with V-4 being significantly overabun- dant in heavy elements. The origin of these overabundances is discussed in the context of the evolutionary versus primordial scenario. The three UV-bright stars K 260, K 996 and K 1082 observed in the very metal-deficient globular cluster NGC 7078 are post-horizontal-branch stars, one of them being slightly enriched in s-elements but with a luminosity too low for third dredge-up to have occured. The abundance patterns of K 1082 in NGC 7078 seem to indicate the presence of mild diffusion and a radiative levitation process, already reported in the blue HB stars of M 13 (Behr et al. 1999, ApJ, 517, L135) and NGC 6752 (Moehler et al. 1999, A&A, 339, 537).

A new method for probing the atmospheres of transiting exoplanets

Although atmospheric transmission spectroscopy of HD 209458b with the Hubble Space Telescope has been very successful, so far no atmospheric absorption features have been detected from the ground. Here we present a new method for probing the atmospheres of transiting exoplanets which may be more suitable for ground-based observations, making use of the Rossiter effect. During a transit, an exoplanet sequentially blocks off light from the approaching and receding parts of the rotating star, causing an artificial radial velocity wobble. The amplitude of this signal is directly proportional to the effective size of the transiting object, and the wavelength dependence of this effect can reveal atmospheric absorption features, in a similar way as with transmission spectroscopy. The advantage of this method over conventional atmospheric transmission spectroscopy is that it does not rely on accurate photometric comparisons of observations on and off transit, but instead depends on the relative velocity shifts of individual stellar absorption lines within the same on-transit spectra. We used an archival data set from the UV–Visual Echelle Spectrograph on the Very Large Telescope to apply this method to HD 209458. The amplitude of the Rossiter effect is shown to be 1.7+1.1−1.2 m s−1 higher in the Sodium D lines than in the weighted average of all other absorption lines in the observed wavelength range, corresponding to an increment of 4.3 ± 3 per cent (1.4σ). The uncertainty in this measurement compares to a photometric accuracy of 5 × 10−4 for conventional atmospheric transmission spectroscopy, more than an order of magnitude higher than previous attempts using ground-based telescopes. Observations specifically designed for this method could increase the accuracy further by a factor of 2–3.

Probing the variability of the fine-structure constant with the VLT/UVES

We assess the cosmological variability of the fine-structure constant α from the analysis of an ensemble of Fe  λ1608, λ2344, λ2374, λ2383, λ2587, and λ2600 absorption lines at the redshiftz = 1.15 toward the QSO HE 0515-4414 by means of the standard many-multiplet (MM) technique and its revision based on linear regression (RMM). This is the first time the MM technique is applied to exceptional high-resolution and high signal-to-noise QSO spectra recorded with the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). Our analysis results in � ∆α/α� MM = (0.1 ± 1.7) × 10 −6 and � ∆α/α� RMM = (−0.4 ± 1.9 ± 2.7sys) × 10 −6 , which are the most stringent bounds hitherto infered from an individual QSO ab- sorption system. Our results support the null hypothesis � ∆α/α� = 0 at a significance level of 91 percent, whereas the support for the result � ∆α/α� = −5.7 × 10 −6 presented in former MM studies is 12 percent.