V. D. Ivanov

VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way

Original article can be found at: http://www.sciencedirect.com/science/journal/13841076 Copyright Elsevier B.V.

Optical and Infrared Spectroscopy of SN 1999ee and SN 1999ex

We report optical and infrared spectroscopic observations of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both of which were hosted by the galaxy IC 5179. For SN 1999ee we obtained a continuous sequence with an unprecedented wavelength and temporal coverage beginning 9 days before maximum light and extending through day 42. Before maximum light SN 1999ee displayed a normal spectrum with a strong Si II λ6355 absorption, thus showing that not all slow-declining supernovae (SNe) are spectroscopically peculiar at these evolutionary phases. A comparative study of the infrared spectra of SN 1999ee and other Type Ia SNe shows that there is a remarkable homogeneity among the Branch-normal SNe Ia during their first 60 days of evolution. SN 1991bg–like objects, on the other hand, display spectroscopic peculiarities at infrared wavelengths. SN 1999ex was characterized by the lack of hydrogen lines, weak optical He I lines, and strong He I λλ10830, 20581, thus providing an example of an intermediate case between pure Ib and Ic supernovae. We conclude, therefore, that SN 1999ex provides the first clear evidence for a link between the Ib and Ic classes and that there is a continuous spectroscopic sequence ranging from the He-deficient SNe Ic to the SNe Ib, which are characterized by strong optical He I lines.

New Galactic star clusters discovered in the VVV survey

Context. VISTA Variables in the V´oa Lactea (VVV) is one of the six ESO Public Surveys operating on the new 4-meter Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages. Aims. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources. Methods. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated KS-band tile images for stellar overdensities. Subsequently, we examined the composite JHKS and ZJKS color images of each candidate. PSF photometry of 15 × 15 arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed. Results. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solar- metallicity Padova isochrones to the color-magnitude diagrams.

The VMC survey - IV. The LMC star formation history and disk geometry from four VMC tiles

We derive the star formation history (SFH) for several regions of the Large Magellanic Cloud (LMC), using deep near-infrared data from the VISTA near-infrared Y JKs survey of the Magellanic system (VMC). The regions include three almost-complete 1.4 deg 2 tiles located ∼ 3.5 ◦ away from the LMC centre in distinct directions. They are split into 21.0 ′ × 21.5 ′ (0.12 deg 2 ) subregions, and each of these is analysed independently. To this dataset, we add two 11.3 ′ × 11.3 ′ (0.036 deg 2 ) subregions selected based on their small and uniform extinction inside the 30 Doradus tile. The SFH is derived from the simultaneous reconstruction of two different colour‐magnitude diagrams (CMDs), using the minimization code StarFISH together with a database of “partial models” representing the CMDs of LMC populations of various ages and metallicities, plus a partial model for the CMD of the Milky Way foreground. The distance modulus (m− M)0 and extinction AV is varied within intervals∼ 0.2 and∼ 0.5 mag wide, respectively, within which we identify the best-fitting star formation rate SFR( t) as a function of lookback time t, age‐metallicity relation (AMR), (m− M)0 and AV. Our results demonstrate that VMC data, due to the combination of depth and little sensitivity to differential reddening, allow the derivation of the space-reso lved SFH of the LMC with unprecedented quality compared to previous wide-area surveys. In particular, the data clea rly reveal the presence of peaks in the SFR(t) at ages log(t/yr)≃ 9.3 and 9.7, which appear in most of the subregions. The most recent SFR(t) is found to vary greatly from subregion to subregion, with the general trend of being more intense in the innermost LMC, except for the tile next to the N11 complex. In the bar region, the SFR(t) seems remarkably constant over the time interval from log(t/yr)≃ 8.4 to 9.7. The AMRs, instead, turn out to be remarkably similar across the LMC. Thanks to the accuracy in determining the distance modulus for every subregion ‐ with typical errors of just∼ 0.03 mag ‐ we make a first attempt to derive a spatial model of the LMC disk. The fields studied so far are fit extremel y well by a single disk of inclination i = 26.2± 2.0 ◦ , position angle of the line of nodesθ0 = 129.1± 13.0 ◦ , and distance modulus of (m− M)0 = 18.470± 0.006 mag (random errors only) up to the LMC centre. We show that once the (m− M)0 values or each subregion are assumed to be identical to those derived from this best-fitting plane, systematic errors in t he SFR(t) and AMR are reduced by a factor of about two.

The infrared supernova rate in starburst galaxies

We report the results of our ongoing search for extincted supernovae (SNe) at near-infrared wavelengths. We have monitored at 2.2m a sample of 46 Luminous Infrared Galaxies and detected 4 SNe. The number of detections is still small but sucient to provide the first estimate of supernova rate at near-infrared wavelengths. We measure a SN rate of SN NIR = 7:6 3:8 SNu which is an order of magnitude larger than observed in quiescent galaxies. On the other hand, the observed near- infrared rate is still a factor 3 10 smaller than that estimated from the far-infrared luminosity of the galaxies. Among various possibilities, the most likely scenario is that dust extinction is so high ( AV> 30) to obscure most SNe even in the near-IR. The role of type Ia SNe is also discussed within this context. We derive the type Ia SN rate as a function of the stellar mass of the galaxy and find a sharp increase toward galaxies with higher activity of star formation. This suggests that a significant fraction of type Ia SNe are associated with young stellar populations. Finally, as a by-product, we give the average K-band light curve of core-collapse SNe based on all the existing data, and review the relation between SN rate and far-infrared luminosity.

Spectral Energy Distributions of Seyfert Nuclei

We present nuclear spectral energy distributions (SEDs) in the range 0.4-16 lm for an expanded CfA sample of Seyfert galaxies. The spectral indexes (f� / � � � IR) from 1 to 16 lm range fromIR � 0.9 to 3.8. The shapes of the spectra are correlated with Seyfert type in the sense that steeper nuclear SEDs (� fincreasing with increasing wavelength) tend to be found in Seyfert 2s, and flatter SEDs (� fis constant) in Seyfert 1- 1.5s. The galaxies optically classified as Seyferts 1.8s and 1.9s display values ofIR as in type 1 objects, or values intermediate between those of Seyfert 1s and Seyfert 2s. The intermediate SEDs of many Seyfert 1.8- 1.9s may be consistent with the presence of a pure Seyfert 1 viewed through a moderate amount (AV d 5 mag) of foreground galaxy extinction. We find, however, that between 10% and 20% of galaxies with broad optical line components have steep infrared SEDs. Torus models usually adopt high equatorial opacities to reproduce the infrared properties of Seyfert 1s and 2s, resulting in a dichotomy of infrared SEDs (flat for type 1s, and steep for type 2s). Such a dichotomy, however, is not observed in our sample. The wide range of spectral indexes observed in the type 2 objects, the lack of extremely steep SEDs, and the large numbers of objects with intermediate spectral indexes cannot be reconciled with predictions from existing optically thick torus models. We discuss possible modifications to improve torus models, including low optical depth tori, clumpy dusty tori, and high optical depth tori with an extended optically thin component.

Discovery of new Milky Way star clusters candidates in the 2MASS point source catalog

A systematic search of the 2MASS point source catalog, covering 47% of the sky, was carried out aiming to reveal any hidden globular clusters in our Galaxy. Eight new star clusters were discovered by a search algorithm based on finding peaks in the apparent stellar surface density, and a visual inspection of their vicinities yielded additional two. They all are concentrated toward the Galactic plane and are hidden behind up to AV = 20 mag which accounts for their late discovery. The majority of new clusters are associated with H regions or unidentified IRAS sources suggesting that they are young, probably similar to Arches or open clusters. Only one candidate has morphology similar to a globular cluster and the verification of its nature will require deeper observations with higher angular resolution than the 2MASS data.

Testing the AGN-starburst connection in Seyfert galaxies

We use the CO band at 2.3 μm to constrain the populations of young stars in the central regions of Seyfert galaxies. We report new CO band spectroscopy of 46 Seyfert galaxies. In most cases, the observed CO indices appear diluted by the presence of a nonstellar component (most likely, warm dust surrounding the active nucleus). We used JHKL aperture photometry to estimate the nonstellar contribution at 2.3 μm. We successfully corrected the CO band for the dilution for 16 galaxies which were not dominated by the nonstellar component. Comparing with CO indices measured in elliptical and purely starbursting galaxies, we find no evidence for strong starbursts in the majority of these galaxies.

Debris Disks in NGC 2547

We have surveyed the 30 Myr old cluster NGC 2547 for planetary debris disks using Spitzer. At 4.5-8 μm we are sensitive to the photospheric level down to mid-M stars (0.2 M☉), and at 24 μm to early G stars (1.2 M☉). We find only two to four stars with excesses at 8 μm out of ~400-500 cluster members, resulting in an excess fraction 1% at this wavelength. By contrast, the excess fraction at 24 μm is ~40% (for B-F types). Out of four late-type stars with excesses at 8 μm two marginal ones are consistent with asteroid-like debris disks. Among stars with strong 8 μm excesses one is possibly from a transitional disk, while another one can be a result of a catastrophic collision. Our survey demonstrates that the inner 0.1-1 AU parts of disks around solar-type stars clear out very thoroughly by 30 Myr of age. Comparing with the much slower decay of excesses at 24 and 70 μm, disks clear from the inside out, of order 10 Myr for the inner zones probed at 8 μm, compared with 100 or more megayears for those probed with the two longer wavelengths.

Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake’s size (1,420 ± 60 km) and albedo are roughly known, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 ± 9 km (1σ) and 1,502 ± 45 km, implying a V-band geometric albedo pV = 0.77 ± 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4–12 nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 ± 0.3 g cm−3 is inferred from the data.