Abstract
It is likely that a number of Galactic globular clusters remain to be discovered, especially toward the Galactic bulge. High stellar density combined with high and differential interstellar ...reddening are the two major problems for finding globular clusters located toward the bulge. We use the deep near-IR photometry of the VISTA Variables in the Vía Láctea (VVV) Survey to search for globular clusters projected toward the Galactic bulge, and hereby report the discovery of 22 new candidate globular clusters. These objects, detected as high density regions in our maps of bulge red giants, are confirmed as globular cluster candidates by their color–magnitude diagrams. We provide their coordinates as well as their near-IR color–magnitude diagrams, from which some basic parameters are derived, such as reddenings and heliocentric distances. The color–magnitude diagrams reveal well defined red giant branches in all cases, often including a prominent red clump. The new globular cluster candidates exhibit a variety of extinctions (0.06 <
A
Ks
< 2.77) and distances (5.3 <
D
< 9.5 kpc). We also classify the globular cluster candidates into 10 metal-poor and 12 metal-rich clusters, based on the comparison of their color–magnitude diagrams with those of known globular clusters also observed by the VVV Survey. Finally, we argue that the census for Galactic globular clusters still remains incomplete, and that many more candidate globular clusters (particularly the low luminosity ones) await to be found and studied in detail in the central regions of the Milky Way.
Context. The census of star clusters in the inner Milky Way is incomplete because of extinction and crowding. Aims. We embarked on a program to expand the star cluster list in the direction of the ...inner Milky Way using deep stacks of KS-band images from the VISTA Variables in Via Lactea (VVV) Survey. Methods. We applied an automated two-step procedure to the point-source catalog derived from the deep KS images: first, we identified overdensities of stars, and then we selected only candidate clusters with probable member stars that match an isochrone with a certain age, distance, and extinction on the color–magnitude diagram. Results. This pilot project only investigates the cluster population in part of one VVV tile, that is, b201. We identified nine cluster candidates and estimated their parameters. The new candidates are compact with a typical radius on the sky of ~0.2–0.4 arcmin (~0.4–1.6 pc at their estimated distances). They are located at distances of ~5–14 kpc from the Sun and are subject to moderate extinction of E(B−V) = 0.4–1.0 mag. They are sparse, probably evolved, with typical ages log(t/1 yr) ~9. Based on the locations of the objects inside the Milky Way, we conclude that one of these objects is probably associated with the disk or halo and the remaining objects are associated with the bulge or the halo. Conclusions. The cluster candidates reported here push the VVV Survey cluster detection to the limit. These new objects demonstrate that the VVV survey has the potential to identify thousands of additional cluster candidates. The sub-arcsec angular resolution and the near-infrared wavelength regimen give it a critical advantage over other surveys.
Abstract
We report the serendipitous discovery of VVV-WIT-12, an unusual variable source that seems to induce variability in its surrounding nebula. The source belongs to the rare objects that we ...call WITs (short for What Is This?) discovered within the VISTA Variables in the Vía Láctea (VVV) survey. VVV-WIT-12 was discovered during a pilot search for light echoes from distant supernovae in the Milky Way using the near-IR images of the VVV survey. This source has an extremely red spectral energy distribution, consistent with a very reddened (
A
V
∼ 100 mag) long-period variable star (
P
∼ 1525 days). Furthermore, it is enshrouded in a nebula that changes brightness and color with time, apparently in sync with the central source variations. The near-IR light curve and complementary follow-up spectroscopy observations are consistent with a variable young stellar object illuminating its surrounding nebula. In this case the source periodic variation along the cycles produces an unprecedented light echo in the different regions of the nebula.
Context.
Interest in searches for extraterrestrial civilizations (ETCs) has been boosted in recent decades by the discovery of thousands of exoplanets.
Aims.
We turn to the classification of ETCs for ...new considerations that may help to design better strategies for searching for ETCs.
Methods.
This study is based on analogies with our own biological, historical, technological, and scientific development. We took a basic taxonomic approach to ETCs and investigated the implications of the new classification on ETC evolution and observational patterns. Finally, we used the quantitative scheme of Kardashev and considered its implications on the searches for ETCs as a counter example to our qualitative classification.
Results.
We propose a classification based on the abilities of ETCs to modify and integrate with their environments: Class 0 uses the environment as it is, Class 1 modifies the environment to fit its needs, Class 2 modifies itself to fit the environment, and a Class 3 ETC is fully integrated with the environment. Combined with the classical Kardashev scale, our scheme forms a two-dimensional method for interpreting ETC properties.
Conclusions.
The new framework makes it obvious that the available energy is not a unique measure of ETC progress: it may not even correlate with how well that energy is used. The possibility for progress without increased energy consumption implies a lower detectability, so in principle the existence of a Kardashev Type III ETC in the Milky Way cannot be ruled out. This reasoning weakens the Fermi paradox, allowing for the existence of advanced, yet not energy hungry, low-detectability ETCs. The integration of ETCs with the environment will make it impossible to tell technosignatures and natural phenomena apart. Therefore, the most likely opportunity for SETI searches to find advanced ETCs is to look for beacons, specifically set up by them for young civilizations like ours (if they would want to do that remains a matter of speculation). The other SETI window of opportunity is to search for ETCs at technological level similar to ours. To rephrase the famous saying of Arthur Clarke, sufficiently advanced civilizations are indistinguishable from nature.
The sky of Chile has the ideal conditions for astronomy worldwide, which has led to crucial scientific development for the country in this and other areas. In the coming years, several space missions ...will occur, the crew members' health being essential for their success. Space medicine studies the changes in human physiology in space, which is entirely altered. It is essential to understand the pathology in the space environment to develop countermeasures to mitigate the different risks, one of the main ones being space radiation, among others. The development of this area of medicine will allow new advances in health on Earth.
ABSTRACT
We present the discovery and multiwavelength characterization of VVV J1438-6158 AB, a new field wide-binary system consisting of a $4.6^{+5.5}_{-2.4}~{\rm Gyr}$ and $T_{\rm eff} = 9500\pm ...125~\mathrm{ K}$ DA white dwarf (WD) and a $T_{\rm eff} = 2400\pm 50~\mathrm{ K}$ M8 ultracool dwarf (UCD). The projected separation of the system is $a = 1236.73~{\rm au}$ ($\sim 13.8\, \mathrm{ arcsec}$), and although along the line of sight towards the Scorpius–Centaurus stellar association, VVV J1438-6158 AB is likely to be a field star, from a kinematic 6D probabilistic analysis. We estimated the physical and dynamical parameters of both components via interpolations with theoretical models and evolutionary tracks, which allowed us to retrieve a mass of $0.62\pm 0.18~\mathrm{ M}_\odot$ for the WD, and a mass of $98.5\pm 6.2~\mathrm{ M}_{\rm Jup}$ ($\sim 0.094\pm 0.006~\mathrm{ M}_\odot$) for the UCD. The radii of the two components were also estimated at $0.01309\pm 0.0003~\mathrm{ R}_{\odot }$ and $1.22\pm 0.05~\mathrm{ R}_{\rm Jup}$, respectively. VVV J1438-6158 AB stands out as a benchmark system for comprehending the evolution of WDs and low-mass companions given its status as one of the most widely separated WD+UCD systems known to date, which likely indicates that both components may have evolved independently of each other, and also being characterized by a large-mass ratio ($q = 0.15\pm 0.04$), which likely indicates a formation pathway similar to that of stellar binary systems.
Context. The severe crowding in the direction of the inner Milky Way suggests that the census of stars within a few tens of parsecs in that direction may not be complete. Aims. We searched for new ...nearby object companions of known high proper motion (HPM) stars located towards the densest regions of the southern Milky Way where the background contamination presented a major problem to previous observations. Methods. The common proper motion (PM) method was used. We inspected the area around 167 known HPM (≥200 mas yr-1) stars: 67 in the disk and 100 in the bulge. Multi-epoch images were provided by the Two Micron All Sky Survey (2MASS) and the VISTA Variables in Via Lactea (VVV). The VVV is a new on-going ZYJHKS plus multi-epoch KS survey of ~562 deg2 of the Milky Way bulge and inner southern disk. Results. Seven new co-moving companions were discovered around known HPM stars (L 149-77, LHS 2881, L 200-41, LHS 3188, LP 487-4, LHS 5333, and LP 922-16); six known co-moving pairs were recovered (LTT 5140 A + LTT 5140 B, L 412-3 + L 412−4, LP 920−25 + LP 920−26, LTT 6990 A + LTT 6990 B, M 124.22158.2900 + M 124.22158.2910, and GJ 2136 A + GJ 2136 B); a pair of stars that was thought to be co-moving was found to have different proper motions (LTT 7318, LTT 7319); published HPMs of eight stars were not confirmed (C* 1925, C* 1930, C* 1936, CD−60 4613, LP 866−17, OGLE BUL−SC20 625107, OGLE BUL−SC21 298351, and OGLE BUL−SC32 388121); last but not least, spectral types ranging from G8V to M5V were derived from new infrared spectroscopy for seventeen stars, members of the co-moving pairs. Conclusions. The seven newly discovered stars constitute ~4% of the nearby HPM star list, but this is not a firm limit on the HPM star incompleteness because our starting point – the HPM list assembled from the literature – is incomplete itself, missing many nearby HPM M- and L-type objects, and it is contaminated with non-HPM stars. We have demonstrated that the superior sub-arcsec spatial resolution, with respect to previous surveys, allows the VVV to examine in greater detail the binary nature nature of known HPM stars. The ≥5 yr span of VVV will provide a sufficient baseline for finding new HPM stars from VVV data alone.
We search for extragalactic sources in the VISTA Variables in the Vía Láctea survey that are hidden by the Galaxy. Herein, we describe our photometric procedure to find and characterize extragalactic ...objects using a combination of SExtractor and PSFEx. It was applied in two tiles of the survey: d010 and d115, without previous extragalactic IR detections, in order to obtain photometric parameters of the detected sources. The adopted criteria to define extragalactic candidates include 1.0 < 2.1 < C < 5; and and the colors: 0.5 < (J-Ks) < 2.0 mag; 0.0 < (J-H) < 1.0 mag; 0.0 < (H-Ks) < 2.0 mag and (J-H) + 0.9 (H-Ks) > 0.44 mag. We detected 345 and 185 extragalactic candidates in the d010 and d115 tiles, respectively. All of them were visually inspected and confirmed to be galaxies. In general, they are small and more circular objects, due to the near-IR sensitivity to select more compact objects with higher surface brightness. The procedure will be used to identify extragalactic objects in other tiles of the VVV disk, which will allow us to study the distribution of galaxies and filaments hidden by the Milky Way.
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