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The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.

Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds1,2. In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated3. Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839–10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10−13s s−1, which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star.

Context.Near infrared (IR) studies of Cepheid variables in the LMC take advantage of the reduced light curve amplitude and metallicity dependence at these wavelengths. This work presents such photometry for two young clusters known to contain sizeable Cepheid populations: NGC 1866and NGC 2031.

We present the Capodimonte Deep Field (OACDF), a deep field covering an area of 0.5 $\deg ^2$in the B, V, Roptical bands plus six medium-band filters in the wavelength range 773–913 nm. The field reaches the following limiting magnitudes: $B_{AB}\sim 25.3$, $V_{AB}\sim 24.8$and $R_{AB}\sim25.1$and contains ~50 000 extended sources in the magnitude range 18 $\le R_{AB} \le 25.0$. Hence, it is intermediate between deep pencil beamsurveys and very wide but shallow surveys. The main scientific goal of the OACDF is the identification and characterization of early-type field galaxies at different look-back times in order to study different scenarios of galaxy formation. Parallel goals include the search for groups and clusters of galaxies and the search for rare and peculiar objects (gravitational lenses, QSOs, halo White Dwarfs). In this paper we describe the OACDF data reduction, the methods adopted for the extraction of the photometric catalogs, the photometric calibration and the quality assessment of the catalogs by means of galaxy number counts, spectroscopic and photometric redshifts and star colors. We also present the first results of the search for galaxy overdensities. The depth of the OACDF and its relatively large spatial coverage with respect to pencil beam surveys make it a good tool for further studies of galaxy formation and evolution in the redshift range 0–1, as well as for stellar studies.

We present optical and near-infrared UBVRIJHKphotometry of stars in the Galactic globular cluster M4 (NGC 6121) based upon a large corpus of observations obtained mainly from public astronomical archives. We concentrate on the RR Lyrae variable stars in the cluster, and make a particular effort to accurately reidentify the previously discovered variables. We have also discovered two new probable RR Lyrae variables in the M4 field: one of them by its position on the sky and its photometric properties is a probable member of the cluster, and the second is a probable background (bulge?) object. We provide accurate equatorial coordinates for all 47 stars identified as RR Lyraes, new photometric measurements for 46 of them, and new period estimates for 45. We have also derived accurate positions and mean photometry for 34 more stars previously identified as variable stars of other types, and for an additional five non-RR Lyrae variable stars identified for the first time here. We present optical and near-infrared color-magnitude diagrams for the cluster and show the locations of the variable stars in them. We present the Bailey (period-amplitude) diagrams and the period-frequency histogram for the RR Lyrae stars in M4 and compare them to the corresponding diagrams for M5 (NGC 5904). We conclude that the RR Lyrae populations in the two clusters are quite similar in all the relevant properties that we have considered. The mean periods, pulsation-mode ratios, and Bailey diagrams of these two clusters show support for the recently proposed "Oosterhoff-neutral" classification.

We have performed accurate iron abundance measurements for 44 red giants (RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival, high-resolution spectra (R? 38,000) collected with UVES at ESO/VLT either in slit mode (five RGs) or in fiber mode (39 RGs, FLAMES/GIRAFFE-UVES). The sample is more than a factor of 4 larger than any previous spectroscopic investigation of stars in dSphs based on high-resolution (R?38000) spectra. We did not impose the ionization equilibrium between neutral and singly ionized iron lines. The effective temperatures and the surface gravities were estimated by fitting stellar isochrones in the V,B- Vcolor-magnitude diagram. To measure the iron abundance of individual lines we applied the LTE spectrum-synthesis fitting method using MARCS model atmospheres of appropriate metallicity. For the 27 stars for which we measured both Fe Iand Fe IIabundances, we found evidence of NLTE effects between neutral and singly ionized iron abundances. The difference is ?0.1 dex, on average, but steadily increases when moving from the metal-rich to the metal-poor regime. Moreover, the two metallicity distributions differ at the 97% confidence level. Assuming that the Fe IIabundances are minimally affected by NLTE effects, we corrected the Fe Istellar abundances using a linear fit between Fe Iand Fe IIstellar abundance determinations. We found that the Carina metallicity distribution based on the corrected Fe Iabundances (44 RGs) has a weighted mean metallicity of [Fe/H] = -1.80 and a weighted standard deviation of ? = 0.24 dex. The Carina metallicity distribution based on the Fe IIabundances (27 RGs) gives similar estimates ([Fe/H] = -1.72, ? = 0.24 dex). The current weighted mean metallicities are slightly more metal-poor when compared with similar estimates available in the literature. Furthermore, when we restricted our analysis to stars with the most accurate iron abundances, ?20 Fe Iand at least three Fe IImeasurements (15 stars), we found that the range in iron abundances covered by Carina RGs (?1 dex) agreed quite well with similar estimates based on high-resolution spectra; however, it is a factor of 2-3 smaller than abundance estimates based on the near-infrared calcium triplet. This finding supports previous estimates based on photometric metallicity indicators.

We introduce a new parameter ??-the difference in magnitude between the red giant branch (RGB) bump and the point on the main sequence (MS) at the same color as the bump (which we call the "benchmark")-to estimate the helium content in old stellar systems. The ?? parameter is a helium indicator, since an increase in helium makes, at fixed age and iron abundance, the RGB bump brighter and the MS benchmark fainter. Moreover, its sensitivity to helium is linear over the entire metallicity range. ?? is also minimally affected by changes of a few gigayears in cluster age, by uncertainties in the photometric zero point, by the amount of reddening, or by the effects of evolution on the horizontal branch. The two main drawbacks of the ?? parameter include the need for precise and large photometric data sets and a strong dependence of the ?Y/?? slope on metallicity. We selected almost two dozen relatively bright Galactic globular clusters (GGCs) with low foreground reddening and a broad range of iron abundance (-2.45 ? [Fe/H] ? -0.70 dex), together with precise and homogeneous multiband (BVI) photometry. The observed ?? parameters and those predicted from ?-enhanced evolutionary models agree reasonably well if we assume a primordial helium content of Y= 0.20 (abundance by mass). The discrepancy becomes ?4? (?B= 0.20 mag) only in the metal-poor regime. Comparison with prescriptions based on a canonical primordial helium content (Y= 0.245 indicates that the observed ?? values are smaller than predicted. These findings support previous results suggesting that current evolutionary models overestimate the luminosity of the RGB bump. The inclusion of envelope overshooting can eliminate the discrepancy. The ?? parameter of GGCs provides an independent detection of prestellar helium, at least at the 5? level.

We present new and accurate radial velocity (RV) measurements of luminous stars of all ages (old horizontal branch, intermediate-age red clump, and young blue plume, as well as red giants of a range of ages: 20.6 ? V? 22) in the Carina dwarf spheroidal galaxy, based on low-resolution spectra collected with the FORS2 multiobject slit spectrograph at the VLT. This data set was complemented by RV measurements based on medium- and high-resolution archive spectra of brighter (V? 20.6) Carina targets collected with the GIRAFFE multiobject fiber spectrograph at the VLT. The combined sample includes more than 21,340 individual spectra of ?2000 stars covering the entire body of the galaxy. The mean (?RV? = 220.4 ± 0.1 km s-1) and the dispersion (? = 11.7 ± 0.1 km s-1) of the RV distribution of candidate Carina stars (?1210 objects, 180 ? RV ? 260 km s-1, 4?) agree quite well with similar measurements available in the literature. To further improve the statistics, the accurate RV measurements recently provided by Walker et al. were also added to the current data set. We ended up with a sample of ?1370 RV measurements of candidate Carina stars that is ?75% larger than any previous Carina RV sample. We found that the hypothesis that the Carina RV distribution is Gaussian can be discarded at 99% confidence level. The mean RV across the body of the galaxy varies from ?220 km s-1at a distance of 7' (?200 pc) from the center to ?223 km s-1at 13' (?400 pc, 6? level) and flattens out to a constant value of ?221 km s-1at larger distances (600 pc, 4? level). Moreover, and even more importantly, we found that in the Carina regions where the mean RV is smaller, the dispersion is also smaller, and the RV distribution is more centrally peaked (i.e., the kurtosis attains larger values). The difference in mean RV is more than 4 km s-1(9? level) when moving from east to west and more than 3 km s-1(?7? level) when moving from north to south. The RV gradient appears to be in the direction of the Carina proper motion. However, this parameter is affected by large uncertainties to reach a firm conclusion. There is evidence of a secondary maximum in RV across the Carina center (|D| ? 200 pc). The occurrence of a secondary feature across the Carina center is also supported by the flat-topped radial distribution based on the photometric catalog. These findings are reminiscent of a substructure with transition properties that are already detected in dwarf ellipticals, and they call for confirmation by independent investigations.

We present deep, accurate, and homogeneous multiband optical (U, B, V, I) photometry of the Carina dwarf spheroidal galaxy, based on more than 4000 individual CCD images from three different ground-based telescopes. Special attention was given to the photometric calibration, and the precision for the B, V, and Ibands is generally better than 0.01 mag. We have performed detailed comparisons in the V, B- V, and V, B- Icolor-magnitude diagrams (CMDs) between Carina and three old, metal-poor Galactic globular clusters (GGCs, M53, M55, M79). We find that only the more metal-poor GCs (M55, [Fe/H] = -1.85; M53, [Fe/H] = -2.02 dex) provide a good match with the Carina giant branch. We have performed a similar comparison in the V, V- ICMD with three intermediate-age clusters (IACs) of the Small Magellanic Cloud (Kron 3, NGC 339, Lindsay 38). We find that the color extent of the subgiant branch (SGB) of the two more metal-rich IACs (Kron 3, [Fe/H] = -1.08; NGC339, [Fe/H] = -1.36 dex) is smaller than the range among Carina's intermediate-age stars. Moreover, the slope of the RGB of these two IACs is shallower than the slope of the Carina RGB. However, the ridge line of the more metal-poor IAC (Lindsay 38, [Fe/H] = -1.59 dex) agrees quite well with the Carina intermediate-age stars. These findings indicate that Carina's old stellar population is metal-poor and appears to have a limited spread in metallicity (?[Fe/H] = 0.2-0.3 dex). The Carina's intermediate-age stellar population can hardly be more metal-rich than Lindsay 38, and its spread in metallicity also appears modest. We also find that the synthetic CMD constructed assuming a metallicity spread of 0.5 dex for the intermediate-age stellar component predicts evolutionary features not supported by observations. In particular, red clump stars should attain colors that are redder than red giant stars, but this is not seen. These results are at odds with recent spectroscopic investigations suggesting that Carina stars cover a broad range in metallicity (?[Fe/H] ? 1-2 dex). We also present a new method to estimate the metallicity of complex stellar systems using the difference in color between the red clump and the middle of the RR Lyrae instability strip. The observed colors of Carina's evolved stars indicate a metallicity of [Fe/H] = -1.70 ± 0.19 dex, which agrees quite well with spectroscopic measurements.

Aims. We report on the unusual distant activity of the dynamically new comet C/2007 D1 (LINEAR), observed at rh= 9.7 AU post-perihelion. This comet is particularly interesting because of its quite large perihelion distance (rq= 8.8 AU).Methods. We analyse Vand Rband images taken at the TNG telescope to characterise the dust coma of the comet and investigate its photometry, colours, and dust production.Results. The colour of the dust is redder than the Sun (V- R= 0.505 ±0.093 at the photometric aperture of radius 2.2”). The Afρvalue is measured to be 1983 ±81 cm for an aperture of radius = 2.2”. An upper limit to the cometary nucleus radius of aN≤18 km is derived. A dust mass-loss rate of $\frac{{\rm d}M_{\rm d}}{{\rm d}t}$= 5.3 × 102kg s-1is measured, which implies that C/2007 D1 (LINEAR) is a very active comet despite its quite large perihelion distance.

Aims. We report on the unusual distant activity of the dynamically new comet C/2007 D1 (LINEAR), observed at rh= 9.7 AU post-perihelion. This comet is particularly interesting because of its quite large perihelion distance (rq= 8.8 AU).