Using photometry and proper motions from Gaia Data Release 2, we detect a 50° long stream of about 70 stars extending westward from the halo globular cluster M5. Based on the similarities in ...distance, proper motions, inferred color-magnitude distribution, and trajectory, we identify this stream as the trailing tidal tail of M5. While the surface density of stars is very low ( 1.5 star per square degree, or 35 mag per square arcsecond), selecting only stars with proper motions consistent with the orbit of the cluster yields a detection significance of 10 . While we find a possible continuation of the stream to 85°, increasing foreground contamination combined with a greater predicted stream distance makes it difficult to detect with current data even if the stream continues unabated. The nonuniform distribution of stars in the stream appears to be consistent with episodic tidal stripping, with the most recently shed stars now trailing the cluster by tens of degrees. We provide a table of the highest-ranked candidate stream stars for ongoing and future spectroscopic surveys.
Abstract
Using photometry and proper motions from Gaia Early Data Release 3, we detect a 45° long trailing stellar debris stream associated with the old, metal-poor globular cluster NGC 7089. With a ...width on the order of 100 pc, the extended stream appears to be as dynamically cold as the coldest known streams found to date. There is some evidence for an extended leading tail extending between 28° and 37° from the cluster, though the greater distance of this tail, combined with proper motions that are virtually indistinguishable from those of foreground stars, make the detection much less certain. The proper motion profile and the path on the sky of the trailing tail are not well matched using a simple Galactic potential composed purely of a disk, bulge, and spherical halo. However, the addition of a moving, massive (
M
= 1.88 × 10
11
M
⊙
) Large Magellanic Cloud brings the model predictions into much better agreement with the observables. We provide tables of the most highly ranked candidate stream stars for follow-up by ongoing and future spectroscopic surveys.
We examine the distribution of old, metal-poor stars in a portion of the recently released PanSTARRs survey. We find an interesting confluence of four new cold stellar stream candidates that appear ...to converge on or pass near the south Galactic pole. The stream candidates, which we designate as Murrumbidgee, Molonglo, Orinoco, and Kwando, lie at a distance of and range in length from to , or about 5 to 33 kpc. The stream candidates are between 100 and 300 pc in width and are estimated to contain between 3000 and 8000 stars each, suggesting progenitors similar to modern day globular clusters. The trajectories of the streams imply orbits that range from hyperbolic to nearly circular. The Molonglo stream is nearly parallel to, at the same distance as, and offset by only from the previously discovered ATLAS stream, suggesting a possible common origin. Orinoco and Kwando also have similarly shaped, moderately eccentric, obliquely viewed orbits that suggest distinct progenitors within a common, larger parent body.
TAILS FROM THE ORPHANAGE Grillmair, Carl J.
The Astrophysical journal,
01/2017, Letnik:
834, Številka:
2
Journal Article
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ABSTRACT Examining a portion of the northern Sloan Digital Sky Survey (SDSS) footprint, we detect at least three and possibly seven halo debris streams. One of these (PS1-D) was recently detected in ...the Pan-STARRS1 survey, and the remaining two are also evident as extensions of the SDSS detections. All of these streams are metal-poor and are found at a distance of around 21 5 kpc. The streams are between 65° and 70° in length, oriented almost north-south, and are nearly parallel and somewhat convergent with the neighboring Orphan stream. Surface densities ranging from 1.5 to 0.5 stars per square degree down to correspond to surface brightnesses between 35 and 37 mag per square arcsecond. The streams each appear to be more than 300 pc across, suggesting either dwarf/ultrafaint galaxy progenitors or long-term heating of very ancient globular cluster streams. The orbits of all but one of these streams appear to be nearly radial, and the orbit normals suggest that all of the streams are part of the Vast Polar Structure, a relatively narrow plane that contains most of the known satellite galaxies, globular clusters, and stellar streams.
The Dark Matter Halo of M54 Carlberg, Raymond G.; Grillmair, Carl J.
The Astrophysical journal,
08/2022, Letnik:
935, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
M54 is a prototype for a globular cluster embedded in a dark matter halo. Gaia Early Data Release 3 photometry and proper motions separate the old, metal-poor stars from the more metal-rich ...and younger dwarf galaxy stars. The metal-poor stars dominate the inner 50 pc, with a velocity dispersion profile that declines to a minimum around 30 pc then rises back to nearly the central velocity dispersion, as expected for a globular cluster at the center of a cold dark matter (CDM) cosmology dark matter halo. The Jeans equation mass analysis of the three separate stellar populations gives consistent masses that rise approximately linearly with radius to 1 kpc. These data are compatible with an infalling CDM dark matter halo reduced to ≃3 × 10
8
M
⊙
at the 50 kpc apocenter 2.3 Gyr ago, with a central globular cluster surrounded by the remnant of a dwarf galaxy. Tides gradually remove material beyond 1 kpc but have little effect on the stars and dark matter within 300 pc of the center. M54 appears to be a “transitional” system between globular clusters with and without local dark halos whose evolution within the galaxy depends on the time of accretion and orbital pericenter.
Abstract
The proper motions of stars in the outskirts of globular clusters are used to estimate cluster velocity dispersion profiles as far as possible within their tidal radii. We use individual ...color–magnitude diagrams to select high-probability cluster stars for 25 metal-poor globular clusters within 20 kpc of the Sun, 19 of which have substantial numbers of stars at large radii. Of the 19, 11 clusters have a falling velocity dispersion in the 3–6 half-mass radii range, 6 are flat, and 2 plausibly have a rising velocity dispersion. The profiles are all in the range expected from simulated clusters that started at high redshift in a zoom-in cosmological simulation. The 11 clusters with falling velocity dispersion profiles are consistent with no dark matter above the Galactic background. The six clusters with approximately flat velocity dispersion profiles could have local dark matter, but are ambiguous. The two clusters with rising velocity dispersion profiles are consistent with a remnant local dark matter halo, but need membership confirmation and detailed orbital modeling to further test these preliminary results.
We analyze all existing secondary eclipse time series spectroscopy of hot Jupiter HD 189733b acquired with the now defunct Spitzer/Infrared Spectrograph (IRS) instrument. We describe the novel ...approaches we develop to remove the systematic effects and extract accurate secondary eclipse depths as a function of wavelength in order to construct the emission spectrum of the exoplanet. We compare our results with a previous study by Grillmair et al. that did not examine all data sets available to us. We are able to confirm the detection of a water feature near 6 mu m claimed by Grillmair et al. We compare the planetary emission spectrum to three model families-based on isothermal atmosphere, gray atmosphere, and two realizations of the complex radiative transfer model by Burrows et al., adopted in Grillmair et al.'s study. While we are able to reject the simple isothermal and gray models based on the data at the 97% level just from the IRS data, these rejections hinge on eclipses measured within a relatively narrow wavelength range, between 5.5 and 7 mu m. This underscores the need for observational studies with broad wavelength coverage and high spectral resolution, in order to obtain robust information on exoplanet atmospheres.
ABSTRACT We examine the repeatability, reliability, and accuracy of differential exoplanet eclipse depth measurements made using the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope during ...the post-cryogenic mission. We have re-analyzed an existing 4.5 m data set, consisting of 10 observations of the XO-3b system during secondary eclipse, using seven different techniques for removing correlated noise. We find that, on average, for a given technique, the eclipse depth estimate is repeatable from epoch to epoch to within 156 parts per million (ppm). Most techniques derive eclipse depths that do not vary by more than a factor 3 of the photon noise limit. All methods but one accurately assess their own errors: for these methods, the individual measurement uncertainties are comparable to the scatter in eclipse depths over the 10 epoch sample. To assess the accuracy of the techniques as well as to clarify the difference between instrumental and other sources of measurement error, we have also analyzed a simulated data set of 10 visits to XO-3b, for which the eclipse depth is known. We find that three of the methods (BLISS mapping, Pixel Level Decorrelation, and Independent Component Analysis) obtain results that are within three times the photon limit of the true eclipse depth. When averaged over the 10 epoch ensemble, 5 out of 7 techniques come within 60 ppm of the true value. Spitzer exoplanet data, if obtained following current best practices and reduced using methods such as those described here, can measure repeatable and accurate single eclipse depths, with close to photon-limited results.
Recent observations of the extrasolar planet HD 189733b did not reveal the presence of water in the emission spectrum of the planet. Yet models of such 'hot-Jupiter' planets predict an abundance of ...atmospheric water vapour. Validating and constraining these models is crucial to understanding the physics and chemistry of planetary atmospheres in extreme environments. Indications of the presence of water in the atmosphere of HD 189733b have recently been found in transmission spectra, where the planet's atmosphere selectively absorbs the light of the parent star, and in broadband photometry. Here we report the detection of strong water absorption in a high-signal-to-noise, mid-infrared emission spectrum of the planet itself. We find both a strong downturn in the flux ratio below 10 microm and discrete spectral features that are characteristic of strong absorption by water vapour. The differences between these and previous observations are significant and admit the possibility that predicted planetary-scale dynamical weather structures may alter the emission spectrum over time. Models that match the observed spectrum and the broadband photometry suggest that heat redistribution from the dayside to the nightside is weak. Reconciling this with the high nightside temperature will require a better understanding of atmospheric circulation or possible additional energy sources.
The Palomar Transient Factory (PTF) is a multiepochal robotic survey of the northern sky that acquires data for the scientific study of transient and variable astrophysical phenomena. The camera and ...telescope provide for wide-field imaging in optical bands. In the five years of operation since first light on 2008 December 13, images taken with Mould-R and SDSS-g′ camera filters have been routinely acquired on a nightly basis (weather permitting), and two different Hα filters were installed in 2011 May (656 and 663 nm). The PTF image-processing and data-archival program at the Infrared Processing and Analysis Center (IPAC) is tailored to receive and reduce the data, and, from it, generate and preserve astrometrically and photometrically calibrated images, extracted source catalogs, and co-added reference images. Relational databases have been deployed to track these products in operations and the data archive. The fully automated system has benefited by lessons learned from past IPAC projects and comprises advantageous features that are potentially incorporable into other ground-based observatories. Both off-the-shelf and in-house software have been utilized for economy and rapid development. The PTF data archive is curated by the NASA/IPAC Infrared Science Archive (IRSA). A state-of-the-art custom Web interface has been deployed for downloading the raw images, processed images, and source catalogs from IRSA. Access to PTF data products is currently limited to an initial public data release (M81, M44, M42, SDSS Stripe 82, and the Kepler Survey Field). It is the intent of the PTF collaboration to release the full PTF data archive when sufficient funding becomes available.
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