A Search for Rr Lyrae Stars in Segue 2 and Segue 3

Boettcher, Erin; Willman, Beth; Fadely, Ross; Strader, Jay; Baker, Mariah; Hopkins, Erica; Ananna, Tonima Tasnim; Cunningham, Emily C.; Douglas, Tim; Gilbert, Jacob; Preston, Annie; Sturner, A. P.

doi:10.1088/0004-6256/146/4/94

Cited by 42 publications

(34 citation statements)

References 62 publications

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“…This approach will not be appropriate for very small UFDs, where fewer than three RR Lyrae stars may be present (e.g., Musella et al 2009;Dall'Ora et al 2012;Boettcher et al 2013, for Ursa Major II, Coma Berenices, and Segue 2 and Segue 3, respectively), or UFDs closer to the Galactic center where the field density of RR Lyrae stars is significant. But for distant Milky Way satellites, this approach seems promising.…”

Section: Resultsmentioning

confidence: 99%

“…We used the general form of the maximum likelihood technique from Boettcher et al (2013) to calibrate our data to SDSS without spatial correction terms, as there are no residual trends in pixel position for the DECam or 90Prime instruments. We determined uncertainties on the zeropoints and colorterms by performing a 1000 iteration bootstrap and added these in quadrature to the photometric uncertainties returned by allstar.…”

Section: Photometry and Calibrationmentioning

confidence: 99%

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Mapping the Tidal Destruction of the Hercules Dwarf: A Wide-field DECam Imaging Search for RR Lyrae Stars

Garling

Willman

Sand

et al. 2018

ApJ

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We investigate the hypothesized tidal disruption of the Hercules ultra-faint dwarf galaxy (UFD). Previous tidal disruption studies of the Hercules UFD have been hindered by the high degree of foreground contamination in the direction of the dwarf. We bypass this issue by using RR Lyrae stars, which are standard candles with a very low field-volume density at the distance of Hercules. We use wide-field imaging from the Dark Energy Camera on CTIO to identify candidate RR Lyrae stars, supplemented with observations taken in coordination with the Beijing-Arizona Sky Survey on the Bok Telescope. Combining color, magnitude, and light-curve information, we identify three new RR Lyrae stars associated with Hercules. All three of these new RR Lyrae stars lie outside its published tidal radius. When considered with the nine RR Lyrae stars already known within the tidal radius, these results suggest that a substantial fraction of Hercules' stellar content has been stripped. With this degree of tidal disruption, Hercules is an interesting case between a visibly disrupted dwarf (such as the Sagittarius dwarf spheroidal galaxy) and one in dynamic equilibrium. The degree of disruption also shows that we must be more careful with the ways we determine object membership when estimating dwarf masses in the future. One of the three discovered RR Lyrae stars sits along the minor axis of Hercules, but over two tidal radii away. This type of debris is consistent with recent models that suggest Hercules' orbit is aligned with its minor axis.

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Section: Resultsmentioning

confidence: 99%

Section: Photometry and Calibrationmentioning

confidence: 99%

Mapping the Tidal Destruction of the Hercules Dwarf: A Wide-field DECam Imaging Search for RR Lyrae Stars

Garling

Willman

Sand

et al. 2018

ApJ

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“…Belokurov et al (2009) presented MMT/Hectochelle spectroscopy of Segue 2 in the discovery paper for the system, which Kirby et al (2013a) supplemented with a large Keck/DEIMOS data set. Imaging of Segue 2 by Boettcher et al (2013) revealed 1 RR Lyrae variable, which was also identified spectroscopically by Kirby et al (2013a). Roederer & Kirby (2014) analyzed the chemical abundance pattern of the brightest RGB member found by Kirby et al (2013a) with a high-resolution Magellan/MIKE spectrum.…”

Section: Appendixmentioning

confidence: 94%

Gaia Proper Motions and Orbits of the Ultra-faint Milky Way Satellites

Simon

2018

ApJ

166

164

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The second data release from the Gaia mission (DR2) provides a comprehensive and unprecedented picture of the motions of astronomical sources in the plane of the sky, extending from the solar neighborhood to the outer reaches of the Milky Way. I present proper motion measurements based on Gaia DR2 for 17 ultra-faint dwarf galaxies within 100 kpc of the Milky Way. I compile the spectroscopically-confirmed member stars in each dwarf bright enough for Gaia astrometry from the literature, producing member samples ranging from 2 stars in Triangulum II to 68 stars in Boötes I. From the spectroscopic member catalogs I estimate the proper motion of each system. I find good agreement with the proper motions derived by the Gaia collaboration for Boötes I and Leo I. The tangential velocities for 14 of the 17 dwarfs are determined to better than 50 km s −1 , more than doubling the sample of such measurements for Milky Way satellite galaxies. The orbital pericenters are well-constrained, with a median value of 38 kpc. Only one satellite, Tucana III, is on an orbit passing within 15 kpc of the Galactic center, suggesting that the remaining ultra-faint dwarfs are unlikely to have experienced severe tidal stripping. As a group, the ultra-faint dwarfs are on highvelocity, eccentric, retrograde trajectories, with nearly all of them having space motions exceeding 370 km s −1 . A large majority of the objects are currently close to the pericenters of their orbits. In a low-mass (M vir = 0.8 × 10 12 M ) Milky Way potential, eight out of the 17 galaxies lack welldefined apocenters and appear likely to be on their first infall, indicating that the Milky Way mass may be larger than previously estimated or that many of the ultra-faint dwarfs are associated with the Magellanic Clouds. The median eccentricity of the ultra-faint dwarf orbits is 0.79, similar to the values seen in numerical simulations, but distinct from the rounder orbits of the more luminous dwarf spheroidals.

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“…Since 2006, about 13 UFDs (with M V > −7) have been reported to contain RR Lyrae variables (Vivas et al 2016, see their Table 4 for a recent compilation), including Boötes I (holding the current record with 15 RR Lyrae stars) and Segue I, one of the faintest UFDs known (Simon et al 2011). It is interesting to note that all dwarf galaxies searched for variable stars so far have at least one RR Lyrae star (Vivas et al 2016; see also Garofalo et al 2013;Boettcher et al 2013;Sesar et al 2014;Medina et al 2017) regardless of the total luminosity.…”

Section: Introductionmentioning

confidence: 99%

RR Lyrae Variables in the Crater II Dwarf Galaxy

Joo

Kyeong

Yang

et al. 2018

ApJ

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We report the detection of RR Lyrae variable stars in Crater II, a recently discovered large and diffuse satellite dwarf galaxy of the Milky Way (MW). Based on B, V time-series photometry obtained with the Korea Microlensing Telescope Network (KMTNet) 1.6 -m telescope at CTIO, we identified 83 ab -type and 13 c -type pulsators by fitting template light curves. The detected RR Lyrae stars are centrally concentrated, which ensures that most of them are members of Crater II. In terms of the distribution of RRab stars in the period-amplitude diagram, Crater II is clearly different from ultrafaint dwarf (UFD) galaxies, but very similar to the two classical MW dwarf spheroidal (dSph) galaxies Draco and Carina with Oosterhoff-intermediate (Oo-int) properties. Combined with the mean period of ab -type variables ( P ab = 0.631±0.004 d) and the c -type fraction (∼0.14) in Crater II, this suggests an Oo-int classification for Crater II and implies that its nature is more like a dSph rather than a UFD. We also estimated the mean metallicity, reddening, and distance of Crater II, from the photometric and pulsation properties of the RR Lyrae stars. The stellar population model we have constructed indicates that Crater II is dominated by an old population, but is relatively younger than the oldest globular clusters in the MW. With a lack of high-amplitude short-period RRab stars, Crater II, like most of the other less massive dSphs, is probably not a surviving counterpart of the major building blocks of the MW halo.

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A Search for Rr Lyrae Stars in Segue 2 and Segue 3

Cited by 42 publications

References 62 publications

Mapping the Tidal Destruction of the Hercules Dwarf: A Wide-field DECam Imaging Search for RR Lyrae Stars

Mapping the Tidal Destruction of the Hercules Dwarf: A Wide-field DECam Imaging Search for RR Lyrae Stars

Gaia Proper Motions and Orbits of the Ultra-faint Milky Way Satellites

RR Lyrae Variables in the Crater II Dwarf Galaxy

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