Nearby Control Fields Research Articles

Observed kinematics of the Milky Way nuclear stellar disk region

Context. The nuclear region of the Milky Way, within approximately −1° < l < +1° and −0.3° < b < +0.3° (i.e., |l|< 150 pc, |b|< 45 pc), is believed to host a nuclear stellar disk, co-spatial with the gaseous central molecular zone. Previous kinematical studies detected faster rotation for the stars belonging to the nuclear stellar disk, compared to the surrounding regions. Aims. We analyze the rotation velocity of stars at the nuclear stellar disk, and compare them with its analog in a few control fields just outside this region. We limit our analysis to stars in the red clump of the color magnitude diagram, in order to be able to relate their mean de-reddened luminosity with distance along the line of sight. Methods. We used a proper motion catalog, obtained from point spread function photometry on VISTA variables in the Vía Láctea images, to construct maps of the transverse velocity for these stars. We complemented our analysis with radial velocities from the 17th data release of the APOGEE survey. Results. We find that the main difference between the nuclear stellar disk region and its surroundings is that at the former we see only stars moving eastward, which we believe are located in front of the Galactic center. On the contrary, in every other direction, we see the brightest red clump stars moving eastward, and the faintest ones moving westward, as expected for a rotating disk. We interpret these observations as being produced by the central molecular zone, hiding stars behind itself. What we observe is compatible with being produced by just the absence of the component at the back, without requiring the presence of a cold, fast rotating disk. This component is also not clearly detected in the newest release of the APOGEE catalog. In other words, we find no clear signature of the nuclear stellar disk as a distinct kinematical component. Conclusions. This work highlights the need for nearby control fields when attempting to characterize the properties of the nuclear stellar disk, as the different systematics affecting this region, compared to nearby ones, might introduce spurious results. Deep, wide field and high resolution photometry of the inner 4 deg of the Milky Way is needed in order to understand the structure and kinematics of this very unique region of our Galaxy.

Are pests adapting to the push-pull system? Ecologically intensified farms in Kenya maintain successful pest control over time

Ecological intensification utilizes biodiversity to maintain agricultural yields while reducing negative environmental impacts. While pest management is a common goal of ecological intensification, studies examining ecologically intensified pest management systems over longer time scales are rare. Using the push-pull system in Western Kenya, we examine whether pest abundance (for both insects and parasitic weeds) and yield vary with time since a given push-pull field was established. With a total of 1880 data points from 476 unique farmers and 24 cropping seasons, we found that pests declined with time since establishment in both push-pull and nearby control fields, while yield improved with time since establishment in push-pull fields. Although this study did not directly address mechanisms, it seems likely that pests in the push-pull system are not successfully adapting to overcome its pest management effects given the continued declines in pest abundance over time. Our data suggest that ecologically intensified agriculture may be resilient against pest adaptation over time, maintaining consistently high yields.

Bees Occurring in Corn Production Fields Treated with Atoxigenic Aspergillus flavus (Texas, USA)

A saprophytic soil fungus, Aspergillus flavus, produces aflatoxin (toxigenic strains) in the kernels of corn (Zea mays L.) and seeds of many other crops. Many strains of A. flavus do not produce toxigenic aflatoxin, and soil application of these atoxigenic strains is a suppressive control tactic to assist in controlling toxigenic conspecifics. Effects of atoxigenic A. flavus applications on honey bees (Apis mellifera L.) and other bees are unknown, and basic information on bee occurrences in cornfields treated with and without this biological agent is needed to inform integrated pest management in corn. Fields receiving atoxigenic A. flavus applications of FourSureTM were compared to nearby control fields in three counties in corn production regions in eastern Texas. In each cornfield, 20 bee bowl traps were deployed along four equal transects located between corn rows, with contents of the bowls (i.e., bees) retrieved after 24 h. Eleven bee genera from four families were collected from cornfields, with only two honey bees collected and zero honey bees observed in transects. The sweat bee genus Agapostemon (primarily composed of the Texas striped sweat bee A. texanus) was most abundant in cornfields (44% of the total number of bees collected), followed by long-horned bees (Melissodes spp., 24%). The southernmost county (i.e., San Patricio) produced over 80% of the total number of bees collected. Bee numbers occurring in cornfields with applications of atoxigenic A. flavus applications were not significantly different from those of nearby control fields. Although not statistically significant, total numbers of bees tended to be lower in FourSure-treated fields than in control fields. More extensive research on bee abundances in relation to the effect of atoxigenic A. flavus is warranted.

The VMC Survey

Context. Detailed studies of intermediate- and low-mass pre-main-sequence (PMS) stars outside the Galaxy have so far been conducted only for small targeted regions harbouring known star formation complexes. The VISTA Survey of the Magellanic Clouds (VMC) provides an opportunity to study PMS populations down to solar masses on a galaxy-wide scale. Aims. Our goal is to use near-infrared data from the VMC survey to identify and characterise PMS populations down to ∼1 M⊙ across the Magellanic Clouds. We present our colour–magnitude diagram method, and apply it to a ∼1.5 deg2 pilot field located in the Large Magellanic Cloud. Methods. The pilot field is divided into equal-size grid elements. We compare the stellar population in every element with the population in nearby control fields by creating Ks/(Y−Ks) Hess diagrams; the observed density excesses over the local field population are used to classify the stellar populations. Results. Our analysis recovers all known star formation complexes in this pilot field (N 44, N 51, N 148, and N 138) and for the first time reveals their true spatial extent. In total, around 2260 PMS candidates with ages ≲10 Myr are found in the pilot field. PMS structures, identified as areas with a significant density excess of PMS candidates, display a power-law distribution of the number of members with a slope of −0.86 ± 0.12. We find a clustering of the young stellar populations along ridges and filaments where dust emission in the far-infrared (FIR) (70 μm–500 μm) is bright. Regions with young populations lacking massive stars show a lower degree of clustering and are usually located in the outskirts of the star formation complexes. At short FIR wavelengths (70 μm,100 μm) we report a strong dust emission increase in regions hosting young massive stars, which is less pronounced in regions populated only by less massive (≲4 M⊙) PMS stars.

Recent star formation at low metallicities. The star-forming region NGC 346/N66 in the Small Magellanic Cloud from near-infrared VLT/ISAAC observations

We perform a photometric analysis on deep, seeing-limited near-IR VLT images of the region NGC 346/N66 and a nearby control field of the SMC in order to locate the centres of active high- and intermediate-mass star formation through the identification of near-IR bright objects as candidate stellar sources under formation.We use archived imaging data obtained with the high-resolution camera ISAAC at VLT of NGC 346/N66 and we construct the near-IR colour-magnitude (CMD) and colour-colour diagrams (C-CD) of all detected sources. We investigate the nature of all stellar populations in the observed CMDs, and we identify all stellar sources that show significant near-IR excess emission in the observed C-CD. We select, thus, the best candidates for being young stellar sources. Based on their near-IR colours we select 263 candidate young stellar sources. This sample comprises a variety of objects such as intermediate-mass PMS and Herbig Ae/Be stars and possibly massive YSOs, providing original near-IR colours for them. The spatial distribution of the selected candidate sources shows that they are located along the dusty filamentary structures of N66 seen in mid- and far-IR dust emission and agrees very well with that of previously detected candidate YSOs and PMS stars. Our study provides an original accurate set of near-IR colours for candidate young stellar sources. While this adds significant information on the star formation process in NGC 346/N66, it is still necessary to reveal the exact nature of these objects, a process that requires the combination of multi-wavelength data, so that complete Spectral Energy Distributions can be constructed for individual sources. This would be a quite important follow-up study to that presented here.

A VERY LARGE TELESCOPE/NACO STUDY OF STAR FORMATION IN THE MASSIVE EMBEDDED CLUSTER RCW 38

We present adaptive optics (AO) near-infrared (JHKs) observations of the deeply embedded massive cluster RCW 38 using NACO on the VLT. Narrowband AO observations centered at wavelengths of 1.28, 2.12, and 2.17 micron were also obtained. The area covered by these observations is about 0.5 pc square, centered on the O star RCW 38 IRS2. We use the JHKs colors to identify young stars with infrared excess. Through a detailed comparison to a nearby control field, we find that most of the 337 stars detected in all three infrared bands are cluster members (~317), with essentially no contamination due to background or foreground sources. Five sources have colors suggestive of deeply embedded protostars, while 53 sources are detected at Ks only; their spatial distribution with respect to the extinction suggests they are highly reddened cluster members. Detectable Ks-band excess is found toward 29 +/- 3 % of the stars. For comparison to a similar area of Orion observed in the near-infrared, mass and extinction cuts are applied, and the excess fractions redetermined. The resulting excesses are then 25 +/- 5 % for RCW 38, and 42 +/- 8 % for Orion. RCW 38 IRS2 is shown to be a massive star binary with a projected separation of ~500 AU. Two regions of molecular hydrogen emission are revealed through the 2.12 micron imaging. One shows a morphology suggestive of a protostellar jet, and is clearly associated with a star only detected at H and Ks, previously identified as a highly obscured X-ray source. Three spatially extended cometary-like objects, suggestive of photoevaporating disks, are identified, but only one is clearly directly influenced by RCW 38 IRS2. A King profile provides a reasonable fit to the cluster radial density profile and a nearest neighbor distance analysis shows essentially no sub-clustering.

CLUSTERING OF RED GALAXIES AROUND THEz= 1.53 QUASAR 3C 270.1

In the paradigm of hierarchical galaxy formation, luminous radio galaxies mark mass assembly peaks that should contain clusters of galaxies. Observations of the z=1.53 quasar 3C270.1 with the Spitzer Space Telescope at 3.6-24 micron and with the 6.5-m MMT in the z'- and Y-bands allow detection of potential cluster members via photometric redshifts. Compared with nearby control fields, there is an excess of 11 extremely red objects (EROs) at 1.33 < z_phot < 1.73, consistent with a proto-cluster around the quasar. The spectral energy distributions (SEDs) of 3/4 of the EROs are better fitted with passive elliptical galaxies than withdust-reddened starbursts, and of four sources well-detected on an archival HST snapshot image, all have undisturbed morphologies. However, one ERO, not covered by the HST image, is a double source with 0.8" separation on the z' image and a marginal (2sigma) 24 micron detection indicating a dust-enshrouded starburst. The EROs are more luminous than L* (H = -23.6 AB mag at z=1.5).

A Search for Stellar Populations in High‐Velocity Clouds

We report the results of a photometric search for stars associated with the cores of four high-velocity clouds (HVCs)—two of which are compact HVCs—using the Las Campanas du Pont 2.5 m and Cerro Tololo Blanco 4 m telescopes in combination with a system of filters (Washington M, T2 + DDO51) useful for identifying low surface gravity, evolved stars. Identical observations of nearby control fields provide a measure of the giant background. Our data reach M0 = 22 for three of the HVCs and M0 = 21.25 for the fourth, depths that allow the detection of any stars within 600 kpc. Although we identify a number of faint late-type star candidates, we find neither a coherent red branch structure nor a clear excess of candidate counts in any HVC. This indicates that the candidates are probably not related to the HVCs and are more likely to be either random Milky Way stars or one of several classes of potential survey contaminants. Echelle spectroscopy of the brightest candidates in one HVC and its control field reveals radial velocities representative of the canonical Galactic stellar populations. In addition to these null results, no evidence of any young HVC stellar populations (represented by blue main-sequence stars) is found, a result consistent with previous searches. Our methodology, specifically designed to find faint diffuse stellar populations, places the tightest upper limit yet on the total stellar mass of HVCs of a few times 105 M☉.

RR Lyrae Stars in M32: Signatures of an Ancient Population

We report the discovery of variable stars in the dwarf elliptical galaxy M32 using a series of images obtained with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The colors, luminosities, and approximate periods of the majority of these stars indicate that they are RR Lyrae stars. Comparisons with the number of such stars identified in a nearby control field reveals that the majority of these variable stars are M32 members and not contaminants from the bulge, halo, or thick disk of the Andromeda Galaxy, M31. This discovery of RR Lyrae stars in M32 provides strong evidence of the presence of an ancient stellar population in this enigmatic galaxy. Although it is not possible with our data to provide a precise age estimate of the population from which the M32 RR Lyrae stars arise, we argue that these stars almost certainly represent a component that is older than 10 Gyr. Due to the sensitivity of the horizontal branch—and therefore the population of the instability strip—to age and metallicity among other parameters, we roughly estimate that this old and metal-poor component represents at least 2.3% of the total stellar population of M32.

The conservation effects of meadow bird agreements on farmland in Zeeland, The Netherlands, in the period 1989–1995

Meadow bird agreements are the most important Dutch agri-environment schemes, both in terms of uptake and of aim. Meadow bird agreements postpone the first agricultural activities on grassland thus reducing egg and chick mortality due to mowing or grazing. We investigated the conservation effects of meadow bird agreements by analysing settlement densities of meadow birds on 34 fields in 1989, 1992 and 1995 in the province of Zeeland, The Netherlands. We compared territory numbers on fields with meadow bird agreements with paired nearby control fields that were conventionally managed. In 1995, the number of territories of black-tailed godwit ( Limosa limosa), lapwing ( Vanellus vanellus) and the total number of meadow birds were significantly higher on fields with conservation management. These differences were partly caused by the higher quality (i.e. higher groundwater level) of fields with meadow bird agreements. Population trends were similar on fields with and without meadow bird agreements and the observed difference in settlement density in 1995 was already present in 1989. Furthermore the effectiveness of the scheme did not increase with time. Thus we found no conclusive evidence that the conservation measures themselves did result in higher territory numbers. Currently, we do not have sufficient ecological and behavioural knowledge of meadow birds to explain why the higher reproductive success does not result in higher settlement densities.

Possible star formation in the halo of NGC 253

We present a deep UBV survey in the direction of the halo of the starburst galaxy NGC 253 aimed at investigating the possible existence of recent star formation far from its disk, as traced by early-type stars. We discuss different classes of objects with blue colors that may contaminate the region of color-color and color-magnitude diagrams occupied by early Population I stars at the distance of NGC 253. Strong upper limits are found on their contribution to the measured object counts by means of models, of surveys of the halo of our Galaxy, and of observations of nearby control fields. A population of objects with $(B-V) 23$ is identified in the direction of the halo of NGC 253 that has no counterpart in the control fields to a high level of statistical confidence. The absolute magnitudes of these objects at the distance of NGC 253 is consistent with them being main sequence B0-B2 stars. The spatial distribution of the bluest objects in the halo of NGC 253 seems to cluster in two groups: one is closer to the disk of NGC 253, and may contain runaway stars expelled from its disk. The other group has projected distances to the plane of the galaxy ranging between 9 and 15 kpc, and at least its base coincides with a peak in radio continuum due to synchrotron emission of cosmic rays escaping the galactic disk. We hypothesize that the distant group of blue stars in the halo of NGC 253 is a result of the interaction between the superwind produced at its nuclear starburst (and perhaps also in star forming regions in the disk) and cold gas in the halo, in a phenomenon similar to the star formation near Centaurus A induced by the interaction of its jet with a HI cloud. If this is the case, NGC 253 provides an example of the ability of less energetic galactic outflows to trigger star formation in haloes, a phenomenon that may also be responsible for the suspected existence of Population I stars at large distances from the disk of the Milky Way.

Screening for tolerance for iron toxicity

This study identified the appropriate time to visually score rice germplasm in order to select materials having the lowest yield reduction under iron toxicity. The experiment took place at Korhogo, 9° 22' N 5° 31' W, in northern Cote d'Ivoire, during the wet season (May-Aug 1995) using a randomized complete block design with three replications on an irrigated Ultisol lowland that contained 343 ppm Fe in soil solution at the beginning of the season. Of 28 transplanted, Suakoko 8 and Bouak 189 were tolerant and susceptible checks, respectively, and two O. glaberrima were land races. Each plot of 40 hills had a planted border using the check varieties. The experiment was repeated simultaneously on a nearby control field which was free of iron toxicity.

Foreground Galaxies And The Variability Of Luminous Quasars

In order to look for an amplification bias (AB) by gravitational lensing caused by medium redshift (0.2≲ z ≲ 0.8) clusters or groups of galaxies, we compare galaxy counts in deep CCD images of highly luminous, high redshift QSOs with those in nearby control fields at a distance of 1 deg at the same galactic latitude. The total sample contains 37 objects up to now, from which one field had to be excluded because of a seeing difference between the QSO and control fields.

The optical gravitational lensing experiment: Deep photometry of the Sagittarius dwarf spheroidal galaxy

We present deep CCD photometry of a field in the newly discovered dwarf spheroidal galaxy in Sagittarius (hereafter Sgr), and of a nearby control field. These data (totaling ~3.5 hrs exposure time in V and I) were used to produce color-magnitude (CM) diagrams reaching I ~ 22.3 in both fields. After statistically removing the field-stars from the CM diagram we find that Sgr is dominated by a moderately old (age ~ 10 Gyr) population, significantly younger than a typical globular-cluster population. There is some evidence for a weak intermediate-age component or alternatively a population of blue stragglers. These results confirm that Sgr is a bona fide dwarf spheroidal (dSph) galaxy, the ninth found orbiting the Milky Way. We have discovered nine short-period variables in the Sgr field, well in excess of the number found in the control field. Seven of these stars have similar apparent magnitudes and are almost certainly RR~Lyr stars in Sgr. We have used the minimum-light colors of the RRab variables to determine the reddening of the Sgr field to be E\vi = 0.22. For an assumed RR~Lyr luminosity of M_V = +0.6 we conclude that the distance of Sgr is 25.2 +/- 2.8 kpc. The properties of the Sgr giant branch and upper main sequence are consistent with a mean metallicity of [Fe/H] ~ -1.1 +/- 0.3.